[prov356]

I think we'll need some more info.

Tank size?

Tank occupants?

Current filtration?

How long has the tank been set up?

Have you tested for nitrate, and if so, what did it measure?

 

[prov356]

The jack dempsey's will outgrow that tank in short order. Before worrying about water changes and substrate I'd return them for something more appropriate for that tank size. There are dwarf cichlids and tanganyikan shell dwellers that'd be a better option.