New cycle questions

marshallsea

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?

AbbeysDad

In any/every tank there becomes a balance of the various bacteria relative to the bio-load. And when we speak of beneficial bacteria, it goes beyond just nitrosomonas and nitrobacter/nitrospira, but also include the facultative bacteria that decomposes waste. These bacteria can be equally dispersed between filters, substrate and decor or may predominantly be in one place or another.

For instance, lets assume there is beneficial bacteria in the filter and the substrate. But then the filter is thoroughly cleaned, eliminating that bacteria. A mini cycle results and the colony expands in the substrate. To a degree, this inhibits BB development in the filter as the substrate colony now processes all of the food.
The filter may grow another colony, but it will likely grow very slowly and may never be what it once was.

In your example of turning filters off is another example of an environmental upset to the balance. The balance can be temporarily upset in any tank, no matter how well established. The established tank just has a better chance of a faster recovery with less calamity when the system re-stablizes.

marshallsea

I see. As always, thank you Abbeys Dad.(The Knight of nitrates).