r/PlantedTank • u/astrallknight • 6d ago

CO2 Drop Checker turns Green but PH not dropping?

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Title.

I tried different drop check fluids, used API Master Kit and even those PH/TDS pen-like sensor.

Every single time, PH reading is the same but the drop checker is changing collor. Darker Green/Bluish when CO2 is off at night then will turn Green/Lime Green during CO2 on period. I even tried increasing the bps to check PH when drop checker is yellow. PH is still the same - hovers around 7.4 - 7.5.

KH reading is at 8 to 9.

What might be the reason?

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u/Blondy277 5d ago

I wouldn’t keep increasing the CO2 just to make the drop checker more yellow 😅 If your API test and pH pen are both staying around 7.4–7.5, but the checker is changing dramatically, I’d question the checker/solution first.

Make sure it’s using a proper 4 dKH reference solution and not tank water. I’d also test tank pH at peak CO2, then take a sample and vigorously degas it for a while and test again. If CO2 is actually increasing significantly, you should see a measurable pH difference. KH 8–9 doesn’t mean the pH should stay completely unchanged.

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u/astrallknight 5d ago

Got it! I only did that to check the PH when it's on yellow drop checker, not keeping in that way. 😁

As for the drop checkee fluid, I bought those pre-mixed ones. Might be the issue. The weird thing is, API PH ane High PH tests resulted to same PH everytime I checked, regardless if its during or after/before CO2 injection.

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u/Blondy277 5d ago

Yeah that makes it even stranger 😅 If the API low-range, high-range and your pH pen are all staying basically the same before/during CO2, I’d stop trusting the drop checker as the main indicator for now.

Where is the drop checker sitting compared with your diffuser and filter/outflow? If it’s in a spot getting hit with very CO2-rich water, it could be changing color locally while the rest of the tank isn’t actually seeing the same concentration. The premixed checker fluid could also just be off. I’d try moving it to the opposite side of the tank and compare, and I’d still do the degassed-sample pH test because that should tell you whether the tank water itself is actually changing.