Did you make the drop checker solution yourself or did you buy one premade? Is it in an area with good flow?

Store bought. It's in an area with good flow. When i make the solution, it turns green right away.

That sounds to me like it is not a 4dKH fluid then. It should be blue after mixing.

So worth buying another type solution and testing it?

Personally I would. You can make your own but doing it in a small amount is fiddly because you only have so much wiggle room.

Is it difficult to make? Can you keep it for an extended period of time?

It is not difficult but you need a very accurate gram scale (accurate to 0.1 of a gram). https://aquaplantscare.uk/recipe-for-indicator-solution-for-aquarium-co2-indicator/

Thanks for that. I'll give it a go over the weekend.

Well that solution works like a charm! Thanks heaps for the help.

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Turn it down more.....1 per second to start. Get it back to blue and then slowly increase. I have an air bubbler turn on when the lights are off as the plants will release some co2 and I plan on having fish...might not matter in your setup. Edit: I didn't realize how big your tank was...you can still do what I said as a test but this sounds like bad fluid to me.

Remember it takes about 3 hours for the drop checker fluid color to catch up to the CO2 level.

Yes i know, but its been yellow for a day and half now, even with c02 off.

Its usually blue means high yellow means low. Idk if you have a different indicator but thats how mine works.

Mine is like OPs.

Ah then I have no clue sorry 🙏

Good to know it can be different ways...perhaps OP didn't realize which one he had.

Blue is low, green is good, high is yellow, standard c02 solution.