KH, pH, and CO2 additions

[SinkyShippy]

I'm currently working on setting up a new 40 gallon tank. The tank will be heavily planted with some plants requiring CO2 additions. Our KH is 2.4 and our pH is 6.8-6.9.

Complicating matters is I plan on adding some fish that need high oxygen content, such as hillstream loaches and panda garras, which CO2 will reduce. It is my understanding that the CO2 capacity in the tank will be significantly reduced because of the kH and PH, which would otherwise allow for greater CO2 additions impacting the oxygen content less. But if this is incorrect please tell me.

In order to raise KH and pH, I have two options: Crushed coral or Seachems Alkaline Buffer. From my understanding Crushed coral automatically increases pH to 8.2 which is too high for the fish we want. Seachem increases it between 7.2-8.5. Anything from 7.2-7.5 is probably good for the fish we want.

My question is, how do I balance this? Should I use crushed coral or Seachem to increase pH/KH? Is CO2 even possible with my tank? How long does the pH stay at a number if I choose to dose Seachem? Does Seachem need to be dosed daily?

Fwiw, I do not have any interest in making RO water. I had to do that with my SW tank and that's why I left that side of the hobby to begin with.

 

[Frank the Fish guy]

C02 and 02 are independent. You can use high aeration to get 02 up, and pump high C02 and get good C02. No worries.

Also KH and GH are independent. You can adjust at will. You can easily raise KH by just adding some baking soda.

Crushed Coral only dissolve below a pH of 7.0 and then stops dissolving. It regulates your pH to be 7.0.

 

[MacZ]

C02 and 02 are independent.

Also KH and GH are independent.

From each other, respectively. Don't dumb it down too much, then things get lost.

CO2 and KH are in a dependent correlation with pH.

@ the OP:
You have still 2.4 °KH, and unless you inject CO2 this is absolutely enough to keep the pH stable.
You have a third option instead of raising KH to raise pH: Add a small amount humic substances (colloqually known as "tannins") to buffer in the lower pH-ranges and stick to plants that don't need high CO2 levels. I would not compromise the fishes needs for the needs of other fish or plants, because combining non-compatible lifeforms falls back on human wants and needs which I deem absolutely secondary in fishkeeping and tbh any kind of animal care.
If you use appropriate current and water movement for these fish you will drive out CO2 anyway in significant amounts, no matter what KH you have.