| Oyster shell is used to help buffer one's ph and add a bit of hardness to help develop the GH which contributes to helping the black appear.
At this stage, it would be good to know one's water parameters so that they could see if their water was "soft" or hard?
even if you don't have a pond. buy a test kit and run a series of pH KH GH on what will be your source water. might be educational. |