My tank has been running for 8 months and has 4 small platy fry, 1 male swordtail,1 BN pleco, wood, a snail population and 12-15 plants or bunches of plants. I feed the day fish 1-2 minutes worth of NLS small pellets once a day and the pleco NLS algae wafers 3 times a week, removing the remainder and snails attached in the morning. I also feed the pleco veggies 2-3 times a week. Under good conditions I change 25% water once a week, vacuuming gravel around the plecos hangout spots. 50% wc monthly vacuuming gravel heavily. Water is usually amm-0 nitrites-0 nitrates10-15. I have 2 hob filters. Twice I have left filters off overnight and awoke to a heavy white fog, I assume to be a bacteria bloom, with fish glancing. Amm- something over 0, nitrites -0, nitrates 10-15. I would expect an established tank to be more stable than that. Is this normal? If not, what could I be doing wrong?