[fredyk]

There is one area about which I am uncertain, pertaining to CO2 and calcium.

Salwater aquarists use CO2 for calcium reactors. So one would think that CO2 is having an effect on calcium in our freshwater planted tanks, dissolving the calcium.

How does this affect the water hardness, and how would it affect snails and shrimp?
For example, I do weekly water changes and use CO2, but the nerites snails shells have large fissures in the shell, and so have been moved to another tank without CO2.
Does one need to add calcium, oyster-coral shells, or do water changes to compensate for dissolved calcium? I'm just curious about the relationship about CO2 and calcium disolving.

 

[KevinC]

In short, yes, CO2 will accelerate the dissolving of calcium salts (like limestone and snail shells).

Longer: other than the snail shells, you don't need or want anything else in the tank that is made of calcium salts. As it dissolves it will raise the GH (and KH if limestone). This is somewhat uncontrolled - and makes it more difficult to control your CO2 level using a pH controller. If you have a level of 3 or more dGH, your snails will survive and you probably have enough Ca for the plants - though your Mg might be a little low if you are only at 3dGH.

Kevin

 

[Rex Grigg]

Reef tanks need a continual supply of calcium because that's what reefs are made of. If you let the calcium supply in a reef tank drop too low many bad things happen, like expensive livestock dying.

That's just not the case in a FW planted aquarium. In fact most people can supply plenty of calcium in a FW planted aquarium by just doing a water change.