pH fluctuations while fishless cycling?

Plaster of paris is gypsom heated to remove water. It disolves better in water than gypsom. Its also generally more pure.

pH in a tank genrerally gets more acidic as time goes by. How much depends upon the buffering capacity. This is why water changes are needed to try to keep stable water conditions even in a planted tank when the nitrates are removed from the tank.

In a practice keep up with the proper maintenance of the tank and put the pH test away for now. The CaSO4 is only for invertabrates. So don't worry about it.

PattyCakes81 said:

Can it be that the pH is lowering because I am cycling? Will it stay like that or when it is finished cycling it would go back to normal?
I let water stand in a cup from the tap for 24 hrs. And it read 7.0.

People say about crushed coral in the filter to help with the pH. Also I heard to add CaSO4 too.But which form of Calcium Sulfate they mean, plaster of Paris or gypsum?

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Your cycle is not dropping the PH. Something in your tank is. If it stabilize at 6.4--that would be OK.

CaSO4 will add buffers to stabalize your PH.

What is currently in your aquarium? Certain driftwood could do this if they are new. Are you using RO/DI water? I had this problem trying to cycle a potential altum anglefish tank and had to resort to buffers. Nitrification is impeded when the pH approaches 6.5. but doesn't stop. It just takes longer. Some well water has a high co2 content at first but is usually blown off by water circulation. Buffers? Ken