I have a 75gal FOWLR. I have a purple tand, small lion, gobie, figi puffer and a stars & strips puffer and a snowflake eel. I did a water change last night (15gal). I used RODI water and now I see today they are breathing very rapidly. I tested the water and everything seems fine. Just the nitrates are between 20 - 50ppm. Anything that i can do?