hello. My tank is a working progress because it has nio lid but after tomorrow it should have two 20 gallon lids. After that I have to buy plants some more decorations and the pirrahna. How do I put a picture of it on here ?
piranhas will destory most of the plants especially when they get bigger.
so if you decide to put real plants in the tank make sure pick the plants that can handle abuse.
Piranhas are ok with both sand or gravel, I don't think they care but with sand you'll see all the bio-waste on the surface layer. gravel will have more gap in between to hide all those waste.
if you'll use gravel then I would recommend a undergravel filter to keep the water clean since piranhas eats meat/feeder, which means lots of bio-waste will sink to the bottom of your tank.
guppies are ok when the piranhas are small, you can try to get large size feeder gold fish when your piranhas get larger or feed them some meat once a while.
I would also recommend getting a small tank for your feeder fishes because they may carry diseases or parasites from pet store or wherever you buy them from. with a smaller tank you can treat the feeders or make sure they are free of those bad stuff before you introduce them to your piranhas.