Looking for piranha advice

[GoingPostal]

I'm a noob when it comes to freshwater, I am restarting my 135 gallon as a piranha tank, right now it's saltwater so got a couple of questions. I need to take down the current setup and purchase anything I need to run freshwater, change my lights and filtration so it'll be awhile before I get the fish.

Planning on red bellies, what's a good number for this size tank, no upgrades planned, I've seen pretty varied numbers and don't want to overstock.

Tank currently has aragonite sand, not sure if it's ok to use with freshwater or if I should change it out

What's a reputable place to order piranha from? Most of my fish come from live aquaria but they don't carry them, also where do you find large pieces of driftwood?

 

[mkturklol]

if your dimensions are 72x18x24 I would reccomend 5 adult rbp. and by adult i mean 10". if you are going to start out any smaller i'd say 7 is a good number imo. I would take out the aragonite sand for 2 reasons. 1 it raises ph and they like 6.5-6.8 and 2 they do kick up alot of sand and i hate cleaning sand out of my canister filter, personally

 

[GoingPostal]

Thank you for responding! Do you run bare bottom then? Or gravel? I am planning on getting small ones, I've heard they will pick some of each other off often, is that why to start out with more of the smaller ones?