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My CO2 Mystery

743 Views 5 Replies 4 Participants Last post by  Manwithnofish
Here is my problem in my 75 gallon tank. I have CO2 injection in my tank controlled by a pinpoint pH controller, but the controller never turns on. The pH never fluctuates (pH stays around 6.9); therefore never turning on CO2 injection. My KH is 4-5. By using the chart I should have perfect CO2 levels, but that cant be true…can it??

I spend 7 hours in the same room that my tank is in and I know the CO2 never turns on. Water changes are done by RO water on an irregular basis. Typically after water changes I wait a day to check KH and GH. My KH never needs adjustments, GH typically does. I adjust my GH with Seachems Equilibrium.

Other tank spects:

pH is always around 6.9
pH prob is Calibrated once a month
Substrate is Eco Complete
Filter is Eheim 2226, hasn’t been cleaned in 3 months
Fish: 7 Angelfish, 10 neons, 1 oto.
Plants; Hair grass and Anubias
Ferts: I follow Seachems chart, but I do not add Excel

Tank history: This tank has been up and running for 4 years. I had it run for about 3 years. I then emptied it and it sat empty for 8 months. When it was empty of water the substrate and driftwood sat in the tank. The driftwood totally dried out and the substrate stayed slightly moist.

My big question is why does my pH stay stable at 6.9. What is causing my pH to stay around 6.9?

My plants are starting to suffer


Thanks in advance.

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It might be that your water tap water is 6.9 or your substrate just keeps it there. The charts just measure dissolved solids. They assume that all your dissolved solids are Ca and mg. There are many other dissolved solids that could be in your water. SO you can't use the charts.

You know two things:
1. your pH stays at 6.9
2. your plants use CO2 and aren't getting enough as they are suffering.

You need to use a drop checker. It will be able to tell you if you have 20-30 ppm of CO2 in your water (you fill it with 4dkh water). Then you can set your CO2 to maintain the drop checker to a green color by setting your ph controller lower and lower until it turns green. That is a starting place. From there you can continue to increase the CO2 until your fish tell you it's enough. Do not increase past green unless you are home to monitor your fish.

My pH monitor is set at 5.8. It give me a yellow to clear color in my drop checker and the plants are thriving. All my fish are fine. I have 3 varieties spawning in my tank. I do regular 50% water changes on Sunday. My CO2 comes on every day for a little while.
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Will my pH drop too low though??

Thanks for the reply!
Will my pH drop too low though??

Thanks for the reply!
Don't worry about the pH. The drop in pH due to CO2 doesn't effect fish IME. I run my tanks on pure RO water with 0dKH and 3dGH and use drop checkers to monitor CO2 levels at 30ppm. The fish are all fine and breeding!
The only thing that I have seen suffer due to low pH has been my snails. The acid water melts their shells away. The plants and fish are thriving. My shrimp are thriving. When I add new fish to the tanks they also do well. I think the pH thing has been overestimated in the past.
The only thing that I have seen suffer due to low pH has been my snails. The acid water melts their shells away.
Yeah, I've noticed my shell has been melting too.

Anyway, I would drop the target pH just to make sure the thing is working. If you drop it to 6.2, that should kick it on, shouldn't it?
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