got a 55 gallon FISH ONLY tank and i set it all up with store bought water and salt and everything was good i took a water sample in to get tested everything was good and they said i was ready to put in some fish so i got 6 damsels to cycle the tank 2 domino black 4 striped and 2 yellow tails. is it alright to add a penquin to help the current or using a canister filter enough for a good current. the canister it for up to 55 gallon tanks. also should i use one of those air filter guys to add bubble to the tank? i tried to test the water with the hydrometer and this morning the reading was good and all of a sudden the reading jumped up on me. is this due to adding the peguin ad the air filtration into the tank? please help do not want to kill the fish. any help is greatly appriciated