I use your regular old clay pots found at most nurseries/plant store.
Of course I break them up and use them as hiding places for my fish.
But it is important that you treat them before you place them in the
Apparently during manufacture some chemicals are used that will leech
out into the water. This can be solved by soaking the pots in with
Canadian Peat (a kind of shreaded wood fiber potting mix/additive,
most garden places have it, I use it for my roses for preventing the
soil from packing and roses like their soil a little acidic, which
the peat adds). Make sure you get the right kind. Soak for a day or
two and rinse. I've also heard that old pots that have had plants in
them for a while have also leeched out the chemicals and are