It sounds like you added 5 HUGE waste producers to a 55 gallon tank before it had completed the
nitrogen cycle.
What are the readings for
ammonia &
nitrite? Is the
nitrate reading still 3?
Most here recommend the
API Master
test kit (liquid), for freshwater, which includes all these tests. The water cloudiness is probably a bacterial bloom, which is good, just indicates your still cycling, and need to be doing daily water changes, depending on your water tests of between 25 & 50%.
It is my feeling that even with your increased filtration, that a 55 gallon tank is not enough to handle these 5 fish. If the pleco is a common, it alone needs to be in a 75 gallon tank. I had one in a 55 for awhile, and the mess was horrid. Piranha, as you know are also messy fish, and the process of feeding goldfish is adding to the problem. I do not feel the cloudiness will clear until the cycle is finished, and you deal with the overcrowding. Good Luck