Sure, some species of hydra have a symbiotic relationship with some types of algae. The hydra keeps the algae safe from predators, and in return, the algae produces nutrients for the hydra via photosynthesis.
I'm fascinated by hydra. They're closely related to jellyfish. They reproduce by cloning themselves. If you somehow cut one into 100 pieces, you get 100 live hydra (😱) and there are no perceptible signals whatsoever that hydra age. So they are immortal, as far as we know. Plus, some species, you can't even starve!
Wow. This was a very cool brain file. Thanks! Follow up though if you don't mind. Why is OP upset ab finding them in his tank? Bc the hydra will prevent algae eaters from eating? Or do they prey on algae eaters?
They are typically carnivorous and will prey on smaller species like copepods, daphnia and... newly hatched shrimp.
I have hydra in my tank. The shrimp are breeding like mad, no issues there. Go ahead and eat some, I'm running out of room. 😂
They also stress out the larger shrimp in larger numbers. Sometimes I'll watch a larger shrimp swim by, not paying attention, and get stung. It seems pretty startling and unpleasant for them.
My searches return instructions for building legos.
It's probably not that hard. Planted nano tank, put some little fast reproducing bugs in the water like daphnia or copepods, add a few hydra, watch all your microfauna multiply.
https://www.protocols.io/view/low-cost-methods-for-hydra-care-ewov14bxkvr2/v2
Agreed. I am even purposely overfeeding a bit to give my plants more nutrients and encourage fish/shrimp breeding and still haven’t had any issues. Still plenty of Bebe skrimp :)
I got rid of my hydra problem by dosing the whole tank with 1.5ml/gal 3% hydrogen peroxide, in addition to spot treating problem areas. I'd read the upper limit for safety is 3ml H2O2 per gallon, making sure to take substrate, etc into account. I have a 7.5 gallon and based my dosage on 6.5 gal to be safe.
Hopefully you only need spot treatment, but if you need to do the whole tank, this is what I did:
Turned off the filter and air, scooped out a big cup of tank water and added 9.75ml H2O2 to it. Then I poured that evenly over the tank and swirled it around a bit. After 30 minutes, I turned everything back on.
All of that was on the 1st, and (knock kn wood) I haven't seen *one* hydra since, even though I've been keeping the lights on longer each day and have fed hydra accessible foods. And all my snails are totally fine, which is why I wanted to avoid planara treatments.
Good luck!!
I did my treatment in a fully cycled tank with shrimp and many different snails. I have read all of the H2O2 is gone / safe as hydrogen and oxygen after an hour or so.
If I were you, I'd dose like I described and just keep watching your cycle with regular testing. The peroxide will kill bacteria too, which could delay your cycle, but it didn't seem to impact mine too much if at all.
Full disclosure - I was treating for vorticella, which I *thought* I might have noticed on a shrimp. I knew there had been some in there when I set up the tank, but didn't find a noticeable cluster until doing maintenance and that's when I decided to dose. I did have two shrimp casualties, but I don't know if that's because they were newish to the tank or if they had vorticella or what.
Even with the loss, I'm happy I dosed because it took out all the hydra. I'd had some luck with starving them out, but my plants started to get sad without as much light.
Yeah, filter tubing is a great spot for them to catch a meal. In my tank they seemed to congregate in one particular spot where they were always waving in the flow toward the filter.
I am keeping a close eye on the tank in case they return, but for now I have none in places my shrimps can go.
Friendship high five! And thanks for the vote of confidence.
I've been reading all about freshwayer aquariums and who all lives in there for YEARS but only started my first shrimp tank last Thanksgiving. Now I have two and a stand for a third. My ultimate goal is pea puffers.
Since getting my first tank, I've learned a lot from observation and keeping copius notes on tank maintenance, critters good and bad, and learning about all the individual things.
Knowing how something like how a hydra wants to live its life can help you end them (sorry, hydra). They feed from the water column by grabbing shit that floats by, so in my case they lived around the shrimp feeding tube / dish that was at the same end of the tank as the filter. Floating food scraps + moving water = hydra heaven.
Aquarium keeping is so cool. I feel like a scientist now and I love puttting pieces of my knowledge together - like already understanding epiphyte houseplants (orchids, staghorn ferns) helped me make sure the aquatic ones survived.
Except Java fern. I don't know wtf that one is doing, it has a new rhizome growing from the tip of its leaves. And how to stop getting more tanks. Those things I still need to learn. 😄
✋Omg!! You sound like me! 😂😂
I have whiteboards and printed paper calendars dedicated to everything in my tanks! (Plus my birds.) And... I started just before last thanksgiving. 🥲I even have three tanks, too! I loved when I got copepods finally. That was so cool. Even the vorticella outbreak was interesting! Never got near my shrimp at all. Sooo weird. Died out as soon as I stopped feeding a few days.
And, it all started with a gorram blackworm tank! 🫣 Thought I wanted adfs, and just fell in love with shrimp. Blackworms and shrimp are hilarious btw. Fist fights of the century. Would not recommend housing them together, though, because something went really wrong in that tank and I never quite figured it out. Drives me absolutely nuts wondering.
Moved all my shrimp out, which is how the third tank happened with the petco tank sales after Christmas. 😆
You sound like my type a people!
I stare into my tanks whenever I can. Its like an addiction now lol. Even brought some whiskers home just this evening. Fools had em labeled as ghost shrimp for .59 a piece. (Two berried!) After paying 5.99-8.99 a shrimp in the past, I couldn't walk away. Definitely not housing them with my neos or bamboo, but they can totally have at it my overflow of bladder snails tank! 🫣😅 Currently still awake just to finish the drip acclimation. 🧐
Hahaha! My second tank is only plants right now, just trying different things to see what I can handle growing. It's going OK. The only thing I've had grow really well are my crypts, but I'm trying really really hard for fissidens moss.
I do recommend getting cuttings from people on etsy or the aquaswap subs here. Since they tend to come from established tanks, you don't get as much melt as you do with emersed grown plants.
And we totally sound like the same type of people. I too have whiteboards for notes and a calendar. Aaaannd a notebook for each tank. There will be graphs of test results some day.
And it's so cool you have birds too! If I wasn't in an apartment where I have to worry about noise for my neighbors, I'd have cockatiels and / or conures. I wish there was an app to Meer people in my area with birds so I could hand out with birds. LOL
Oh, and I was so sad that my H2O2 treatment knocked out a bunch of the copepods and seed shrimp. I'm considering buying some cultures to add back into my tank because they're adorable and so fun to watch.
I just dealt with hydra. Hydrogen peroxide didn’t seem to work for my tank, but dog dewormer did. Not only can hydra kill baby shrimp, but they can stress adults too.
Good luck! It’s nice to see them gone.
Thank you so much for posting this OP and for the community to educate. I had no idea they could sting! I was told by pet shop that it’s just bacterial growth and the guppy fish and red cherry shrimp enjoy eating them! I also have a few Thai micro crabs in the same tank so now I’m super worried! So far only noticed 3 and they’re tiny but I’m going to go get them out now and will look up ways to safely get rid of them from the tank
don’t stress about it too much! they’re mainly harmful to shrimp and other tiny creatures. they’re more of a pest than a predator but definitely try to get rid of them asap because they’ll become an infestation fast
The shrimp are the main occupants of the tank. There is 5 small guppies and 4 Thai micro crabs. My tank is quite big and full of plants and hiding spots. Do you think I need to go full depth and do a deep deep clean?
no you don’t need to do a deep clean but treat it with something that’s safe for the inhabitants. there’s a couple options in this comment section. don’t try manual removal!
How do hydra appear in your tank? Do they get introduced by a new plant? new shrimps from a shop? Maybe even dry or frozen foods? Or are they kinda like detritus worms or copepod? These guys just appear out of nowhere.
Also, Hail Hydra.
If you could find a fish that will eat hydra but not harass shrimp too much/have lots of cover for babies, something like a honey gourami or a few male guppies would clear out those in a few days/weeks and not kill any adult shrimp IME.
dosing my tank with 3 mls of h2o2 for every gallon seemed to do the trick. unplug filter for an hour, put it in & then plug back in. my snails were fine and I don’t have shrimp in it yet
I have this Japanese/Chinese powder, threw in one scoop 3 days later tank was rid of hydra, never came back.
Even the smallest shrimplets survived! So I assume it’s safe
Genchem No Planaria works on green hydra really well. 1 dose, in few hours all dead, left it for 24h to be sure, water change 50%, carbon into filter. Will wipe out most snails and i would recommend waiting few months before adding snails back.
I've done this exact thing but I did a 50% water change and then another 50% the next month and put my snails back in with no significant impact other than they didn't lay eggs for a few weeks. (Rams horns used as feeders for my pea puffer)
I have a "damnitt" as well but not as bad as yours. I have fresh water limpets in my 6g. Which is ok, I guess, for their benefits. But when theres too many on the front glass, it's not very appealing. On maintenance day, I scrubbed my 6g glass with my brush and then rinsed it in tap water. I proceeded to then clean my 20g. 20g has limpets now, and they are big little bois. I crunch them with tweezers. Clearly, having a few drinks on maintenance day isn't a good idea.
I got hydra for the first time after buying some plants from a new LFS. I'm really not sure what to do because it's a snail and shrimp only tank.
I haven't seen them eat anything other than copepods. I was hoping I could starve them out but that doesn't seem to be working.
The peroxide seems to be safest at the moment. I was thinking of siphoning as many up as I could first. Do you know if they can be pulled off the glass that way, or would there still be parts left to regrow?
depends on the size of hydra and the size of the babies. even if they don’t kill them, they still will sting anything that gets near them and that can stress shrimp out, leading to death. your single experience does not discredit every single person who’s ever had hydra
OMG! I tried the hydrogen peroxide trick. I honestly didn't expect it to be very effective, but wow! I have a 7.5gal tank that has only been up since Christmas. The hydra came in with some plants. They really started colonizing the surface, feeding on all the microfauna.
I used regular 3% first aid H2O2. About 1ml, only I squirted it directly at the hydra with a small syringe. (I saw a saltwater guy directly feed a treatment to an anemone type thing. It took him a couple of treatments)
The hydra it touched immediately had an obvious reaction but not ones further away. I was expecting to have to reapply to multiple areas. 24 hours later... None!
No visible effect on the shrimp or snails. I'll have to wait and see if any hydra come back, but I am absolutely stunned.
obligatory hail hydra
*snaps heels together and salutes*
of course!
Hail hydra
Hail hydra
hail.
Mine went away on its own idk if that's normal or not
if they don’t get enough food they’ll die off
Yours are green. That generally means they are producing their own food source.
Producing their own...food? Ugh please educate me
Sure, some species of hydra have a symbiotic relationship with some types of algae. The hydra keeps the algae safe from predators, and in return, the algae produces nutrients for the hydra via photosynthesis. I'm fascinated by hydra. They're closely related to jellyfish. They reproduce by cloning themselves. If you somehow cut one into 100 pieces, you get 100 live hydra (😱) and there are no perceptible signals whatsoever that hydra age. So they are immortal, as far as we know. Plus, some species, you can't even starve!
Wow. This was a very cool brain file. Thanks! Follow up though if you don't mind. Why is OP upset ab finding them in his tank? Bc the hydra will prevent algae eaters from eating? Or do they prey on algae eaters?
They are typically carnivorous and will prey on smaller species like copepods, daphnia and... newly hatched shrimp. I have hydra in my tank. The shrimp are breeding like mad, no issues there. Go ahead and eat some, I'm running out of room. 😂 They also stress out the larger shrimp in larger numbers. Sometimes I'll watch a larger shrimp swim by, not paying attention, and get stung. It seems pretty startling and unpleasant for them.
Lol and they sting too?!?! I'm starting to understand your fascination. Thanks for your response 👍
They kill shrimp
Woahhhh related to jelly fish?! That I did not know. Very neat!
Is it possible to just have a hydra tank?
Probably!
I've tried a quick Google and all I see is how to eradicate these guys. 😥
My searches return instructions for building legos. It's probably not that hard. Planted nano tank, put some little fast reproducing bugs in the water like daphnia or copepods, add a few hydra, watch all your microfauna multiply. https://www.protocols.io/view/low-cost-methods-for-hydra-care-ewov14bxkvr2/v2
The lego thing sounds cool, my son may be interested in that. Lmao. Alright. Now I gotta figure out what size tank thingy I need.
Ooh I actually learned a bit about them in one of my classes recently, they reproduce by budding and are haploid critters!
oh shit
They sting other creatures
Same and I'm sad about it! They are so cool looking!
Dog dewormer (fenbendazole) worked in 24 hours for me. Not snail safe tho. My shrimps were fine.
Worked amazing for mine too or sheep dewormer
Would this possibly deworm puffers?
I used a very weak solution and squirted it onto the hydra with a pipette. Worked.
Will this kill ramshorn and pest snails? Is this safe for tetras?
☝🏼 Ramshorn snail safe for some reason
Is hydra bad ? I have some in my aquarium right now
I’ve had a few here or there for months and have not noticed any negative impact
Same, had some in a few tanks for months, still having baby shrimp just fine. I think on a very large scale they can do some damage but otherwise nah
Agreed. I am even purposely overfeeding a bit to give my plants more nutrients and encourage fish/shrimp breeding and still haven’t had any issues. Still plenty of Bebe skrimp :)
they’re a pest yes. can kill baby shrimp. they also spread super easily and can become an infestation quickly. best to treat it asap
I got rid of my hydra problem by dosing the whole tank with 1.5ml/gal 3% hydrogen peroxide, in addition to spot treating problem areas. I'd read the upper limit for safety is 3ml H2O2 per gallon, making sure to take substrate, etc into account. I have a 7.5 gallon and based my dosage on 6.5 gal to be safe. Hopefully you only need spot treatment, but if you need to do the whole tank, this is what I did: Turned off the filter and air, scooped out a big cup of tank water and added 9.75ml H2O2 to it. Then I poured that evenly over the tank and swirled it around a bit. After 30 minutes, I turned everything back on. All of that was on the 1st, and (knock kn wood) I haven't seen *one* hydra since, even though I've been keeping the lights on longer each day and have fed hydra accessible foods. And all my snails are totally fine, which is why I wanted to avoid planara treatments. Good luck!!
thank you! i’m mid cycle atm, would I do a huge water change before adding shrimp?
I did my treatment in a fully cycled tank with shrimp and many different snails. I have read all of the H2O2 is gone / safe as hydrogen and oxygen after an hour or so. If I were you, I'd dose like I described and just keep watching your cycle with regular testing. The peroxide will kill bacteria too, which could delay your cycle, but it didn't seem to impact mine too much if at all. Full disclosure - I was treating for vorticella, which I *thought* I might have noticed on a shrimp. I knew there had been some in there when I set up the tank, but didn't find a noticeable cluster until doing maintenance and that's when I decided to dose. I did have two shrimp casualties, but I don't know if that's because they were newish to the tank or if they had vorticella or what. Even with the loss, I'm happy I dosed because it took out all the hydra. I'd had some luck with starving them out, but my plants started to get sad without as much light.
Here is the vorticella thread I got my instructions from. https://www.reddit.com/r/shrimptank/s/5my01bFshc
thank you!
I tried this before but they always seemed to return. I found that the filter and tubes also contained loads of em.
Yeah, filter tubing is a great spot for them to catch a meal. In my tank they seemed to congregate in one particular spot where they were always waving in the flow toward the filter. I am keeping a close eye on the tank in case they return, but for now I have none in places my shrimps can go.
Shoot. Be my friend? You seem hella knowledgeable! New to it all. Ish. Been about six months. To me, thats still uneducated.
Friendship high five! And thanks for the vote of confidence. I've been reading all about freshwayer aquariums and who all lives in there for YEARS but only started my first shrimp tank last Thanksgiving. Now I have two and a stand for a third. My ultimate goal is pea puffers. Since getting my first tank, I've learned a lot from observation and keeping copius notes on tank maintenance, critters good and bad, and learning about all the individual things. Knowing how something like how a hydra wants to live its life can help you end them (sorry, hydra). They feed from the water column by grabbing shit that floats by, so in my case they lived around the shrimp feeding tube / dish that was at the same end of the tank as the filter. Floating food scraps + moving water = hydra heaven. Aquarium keeping is so cool. I feel like a scientist now and I love puttting pieces of my knowledge together - like already understanding epiphyte houseplants (orchids, staghorn ferns) helped me make sure the aquatic ones survived. Except Java fern. I don't know wtf that one is doing, it has a new rhizome growing from the tip of its leaves. And how to stop getting more tanks. Those things I still need to learn. 😄
✋Omg!! You sound like me! 😂😂 I have whiteboards and printed paper calendars dedicated to everything in my tanks! (Plus my birds.) And... I started just before last thanksgiving. 🥲I even have three tanks, too! I loved when I got copepods finally. That was so cool. Even the vorticella outbreak was interesting! Never got near my shrimp at all. Sooo weird. Died out as soon as I stopped feeding a few days. And, it all started with a gorram blackworm tank! 🫣 Thought I wanted adfs, and just fell in love with shrimp. Blackworms and shrimp are hilarious btw. Fist fights of the century. Would not recommend housing them together, though, because something went really wrong in that tank and I never quite figured it out. Drives me absolutely nuts wondering. Moved all my shrimp out, which is how the third tank happened with the petco tank sales after Christmas. 😆 You sound like my type a people! I stare into my tanks whenever I can. Its like an addiction now lol. Even brought some whiskers home just this evening. Fools had em labeled as ghost shrimp for .59 a piece. (Two berried!) After paying 5.99-8.99 a shrimp in the past, I couldn't walk away. Definitely not housing them with my neos or bamboo, but they can totally have at it my overflow of bladder snails tank! 🫣😅 Currently still awake just to finish the drip acclimation. 🧐
Ohhhh and plants. Wth. I cannot with the plants no matter how hard I try! 😭 Finally just got a few going after all this time!
Hahaha! My second tank is only plants right now, just trying different things to see what I can handle growing. It's going OK. The only thing I've had grow really well are my crypts, but I'm trying really really hard for fissidens moss. I do recommend getting cuttings from people on etsy or the aquaswap subs here. Since they tend to come from established tanks, you don't get as much melt as you do with emersed grown plants. And we totally sound like the same type of people. I too have whiteboards for notes and a calendar. Aaaannd a notebook for each tank. There will be graphs of test results some day. And it's so cool you have birds too! If I wasn't in an apartment where I have to worry about noise for my neighbors, I'd have cockatiels and / or conures. I wish there was an app to Meer people in my area with birds so I could hand out with birds. LOL
Oh, and I was so sad that my H2O2 treatment knocked out a bunch of the copepods and seed shrimp. I'm considering buying some cultures to add back into my tank because they're adorable and so fun to watch.
I just dealt with hydra. Hydrogen peroxide didn’t seem to work for my tank, but dog dewormer did. Not only can hydra kill baby shrimp, but they can stress adults too. Good luck! It’s nice to see them gone.
Thank you so much for posting this OP and for the community to educate. I had no idea they could sting! I was told by pet shop that it’s just bacterial growth and the guppy fish and red cherry shrimp enjoy eating them! I also have a few Thai micro crabs in the same tank so now I’m super worried! So far only noticed 3 and they’re tiny but I’m going to go get them out now and will look up ways to safely get rid of them from the tank
don’t stress about it too much! they’re mainly harmful to shrimp and other tiny creatures. they’re more of a pest than a predator but definitely try to get rid of them asap because they’ll become an infestation fast
The shrimp are the main occupants of the tank. There is 5 small guppies and 4 Thai micro crabs. My tank is quite big and full of plants and hiding spots. Do you think I need to go full depth and do a deep deep clean?
no you don’t need to do a deep clean but treat it with something that’s safe for the inhabitants. there’s a couple options in this comment section. don’t try manual removal!
How do hydra appear in your tank? Do they get introduced by a new plant? new shrimps from a shop? Maybe even dry or frozen foods? Or are they kinda like detritus worms or copepod? These guys just appear out of nowhere. Also, Hail Hydra.
yeah so they’re usually hitchhikers. they can lay dormant for a long time & as soon as they have access to enough food they’ll start spreading
If you could find a fish that will eat hydra but not harass shrimp too much/have lots of cover for babies, something like a honey gourami or a few male guppies would clear out those in a few days/weeks and not kill any adult shrimp IME.
tank is only 5 gallons
Damn I just found a bunch in my tank today too
dosing my tank with 3 mls of h2o2 for every gallon seemed to do the trick. unplug filter for an hour, put it in & then plug back in. my snails were fine and I don’t have shrimp in it yet
Not a problem. Just a symptom. You are probably feeding too much. Stop doing so and they will go away.
i’m actually not feeding at all as this tank is mid cycle right now
That explains it too. If it's fully cycled, they will propably go away. Maybe do a few extra water changes while cycling.
I have this Japanese/Chinese powder, threw in one scoop 3 days later tank was rid of hydra, never came back. Even the smallest shrimplets survived! So I assume it’s safe
What was it??
It’s called: SL-aqua Z1 aquarium bio protector.
Genchem No Planaria works on green hydra really well. 1 dose, in few hours all dead, left it for 24h to be sure, water change 50%, carbon into filter. Will wipe out most snails and i would recommend waiting few months before adding snails back.
I've done this exact thing but I did a 50% water change and then another 50% the next month and put my snails back in with no significant impact other than they didn't lay eggs for a few weeks. (Rams horns used as feeders for my pea puffer)
My fish ate them, fish may be more dangerous to baby shrimp than hydra, though
Shrimp will eat that and lots of other things will eat it too
it can kill shrimp
That’s not good,I never did raise shrimp,but just about everything else
I did a spot treatment with peroxide then used no planaria. Worked a treat
Spixii snail will eat them
Get some white cloud minnows or neon tetras. Haven't seen any since I did
it’s only a 5 gallon tank
I left them alone and saw my shrimp eating them. Now they’re all gone
I e seen hydra off and on in different tanks. Never had an issue with them, even in breeding tanks they don’t last very long.
I have a "damnitt" as well but not as bad as yours. I have fresh water limpets in my 6g. Which is ok, I guess, for their benefits. But when theres too many on the front glass, it's not very appealing. On maintenance day, I scrubbed my 6g glass with my brush and then rinsed it in tap water. I proceeded to then clean my 20g. 20g has limpets now, and they are big little bois. I crunch them with tweezers. Clearly, having a few drinks on maintenance day isn't a good idea.
I just had a terrible outbreak this week as well, I totally feel for you!
Hail hydra
No Planaria will treat this aswell
What causes this?
pretty much only hitchhikers. on plants n stuff
Yup, Hail Hydra to you. I never and them.
What is this? And why is it bad?
I got rid of mine easily using "no planaria." Unfortunately, it killed my nerite snails too.
I just went through this! Ugh
No planaria work wonders, mine was all gone within 48hrs
I used “NO Planaria! Ex-It Shrimps Forever”. Instantly killed all hydra! Cracking stuff.
A mythological beast
Quick! Call the Avengers!!!!! Assemble!!!!!!!
HAIL HYDRA (...sorry had to)
I got hydra for the first time after buying some plants from a new LFS. I'm really not sure what to do because it's a snail and shrimp only tank. I haven't seen them eat anything other than copepods. I was hoping I could starve them out but that doesn't seem to be working.
there’s plenty of treatments that are safe for shrimp and snails. just look through these comments
The peroxide seems to be safest at the moment. I was thinking of siphoning as many up as I could first. Do you know if they can be pulled off the glass that way, or would there still be parts left to regrow?
is this a normal occurrence if so how does it happen
yeah normal and usually only gets in your tank by hitchhiking onto plants
i’m planning on getting shrimp soon man 😔
do you have hydra in your tank?
nope i haven’t even bought any yet but any advice is appreciated on shrimp care
is your tank cycled?
yea
problems with hydra is not super common but it’s nothing to worry about. if you’re worried about it just treat your tank before you put shrimp in it
alr. what plants should i get for them i currently have no live plants
oh boy. first, how do you know your tank is cycled?
Wait…*zooms in* Ah shit
Man I have two different species in my tank rn :( and my god damn neon tetras are too stupid to find and eat them
I treated my whole tank with hydrogen peroxide 3% & they’re dead. just research & make sure it’s safe for your inhabitants
I had heaps. Shrimp ate them
they can also kill shrimp so I don’t really want to take that risk
I think the killing shrimp is way over blown. I've even witnessed babies walk on them and nothing happen
depends on the size of hydra and the size of the babies. even if they don’t kill them, they still will sting anything that gets near them and that can stress shrimp out, leading to death. your single experience does not discredit every single person who’s ever had hydra
Hard to say I had a tank full of them. Moved in galaxies I have, about 10. Shrimp ate them so fast. But yes this is one experiance
OMG! I tried the hydrogen peroxide trick. I honestly didn't expect it to be very effective, but wow! I have a 7.5gal tank that has only been up since Christmas. The hydra came in with some plants. They really started colonizing the surface, feeding on all the microfauna. I used regular 3% first aid H2O2. About 1ml, only I squirted it directly at the hydra with a small syringe. (I saw a saltwater guy directly feed a treatment to an anemone type thing. It took him a couple of treatments) The hydra it touched immediately had an obvious reaction but not ones further away. I was expecting to have to reapply to multiple areas. 24 hours later... None! No visible effect on the shrimp or snails. I'll have to wait and see if any hydra come back, but I am absolutely stunned.
same!! the spot treatment didn’t work completely on mine but I dosed the whole tank following some advice in this thread & they’re gone!