I have a 150 stock tank pond. 6 goldfish. 1 pleco 3 danios <was 5 but the rain overflowed it> I have a 400 gallon per hour pump and filter with fountain. Bioballs, Sponge and Filter element. No gravel. I could do a 100% water change as long as I leave the water and bio balls alone and not start the nitrogen cycle over again correct?


