DragonFish71
Great white snark
Um yeah, piranha grow very fast. I would start looking into that larger tank very soon.
I kept 6 piranha in a 75 gallon for a few years. 75 is not nearly big enough and I had to give up half of them after about a year and ahalf. (I got them at around the size of a nickel)
Even with only 3, I could tell they were depressed in my 75, as they were dull in colour and didn't swim a lot other than when they ate. When they finally died after about 6 years, with only 2 remaining for the last couple of years, I can safely say that you should either upgrade to a 300 gallon tank or make arrangements to give up your fish.
They will be happy in your 55 until they are about 7 inches and then they will begin to become aggressive and you will find fish with large chunks missing.
Also, don't worry about them chewing on anything, all my equipment is submersible and I never had any problems with that.