I have had fish awhile, but would still say I am a novice. I have at present 3 RBP and 1 Pleco in a 400 litre fish tank. I have done all checks on water and everything is fine for PH and Ammonia, nitrites. Nitrates are still high. Just noticed today that I have found quite a bit of white/grey poo, but not sure if it came from the RBP or the Pleco. I have attached a photo. Can anyone see if it would be from an internal parasite or a bacteria. Anything you need to know, just ask!!.
I would keep an eye on them and see if there's any more. It may be just a one-off related to what they've been eating.
I'm assuming by RBP you're referring to red-bellied piranhas? You do realise that they need to either be kept alone or in a larger group of 5 or more and that 400 litres is nowhere near enough for them? It's going to be too small for the plec too when it reaches its adult size. http://www.seriouslyfish.com/species/pygocentrus-nattereri/