Bacteria Die Back

[anon02]

I completed a fishless cycle a month ago and added 6 harlequins and 2 corys to a 50 litre tank, which I reckoned to be about an 80% stocking. Yesterday I transferred the fish to their new tank and tested the Q tank with ammonia prior to adding new stock, well it`s a good job I did, a filter that was processing 5ppm ammonia to double zeros a month ago is now taking 24 hours to process 1ppm ammonia to zero .... strange

 

[JoshuaA]

I would say that if you mean 6 Harlequin Rasboras and 2 Corys that would no where near be 80% of your stocking.

Your filter will either gain or lose bacteria colonies, the idea of the fish-less cylce is to boost the bacteria to it's maximum potential (for a theoretical 100% stocking). In my eyes you've stocked no where near your potential for that tank and the filter bacteria has accommodated by dying back to equilibrium between Bacteria - Ammonia/Nitrite.

I would most definitely say that this is normal for a filter, picture it as you fed a few snails in fact enough to feed hundreds (adding ammonia for the filter). These few snails multiply and create more snails until there is just enough food per snail to survive. Suddenly you drop the feeding to a small amount (replacing ammonia with real fish) all of a sudden your snails (Filter bacteria) aren't receiving the same amount of food and die back to an equilibrium point for enough for per snail.

In effect that is it in a snail form, I just snails because pest snails multiply faster than a chain reaction in a nuclear fission reactor.

 

[Tolak]

5ppm in 24 hours is a replication of an incredibly overstocked tank. Your guesstimation of an 80% stocking level maintaining a bacterial colony that processes 1ppm ammonia in 24 hours is proof of that. 30 harlequins & 10 corys would be an example of incredibly overstocked in that tank, while the filter could handle it in a biological sense the fish would be like bumper cars.

The 5ppm is to create plenty of room for error for the newer fishkeeper. Once you understand this as well as many of the other things that go along with bio filtration, cycling and stocking you can go by what you know.

 

[waterdrop]

Completely agree with Josh and Tolak. A lot of newcomers come in to our beginners section here and get subjected to all of us yakking about 5ppm constantly and then quite easily fall in to the image of 5ppm being the ammonia level produced by a fully stocked tank. It isn't, really. It's a quite large concentration that's really equivalent to considerably above full stocking, even by liberal guidelines I think.

What's so interesting about the chosen 5ppm in RDD's fishless cycling article, I feel, is that it seems to have withstood the test of time quite well as a methodology. I feel it really gets the colony sizes up to a robust enough level that when a first stocking (regardless of whether the first stocking is a full stocking or whether its less) drops off to match the bioload, it is extremely unlikely to subsequently mini-spike or have other problems handling the maintenance of a safe environment for the new fish.

The problem is that complex environmental systems of living things are not very linear in their behaviors. Bacteria don't just smoothly ramp up and down, they do it in jerks and spikes and sudden changes. The fishless cycling methodology that has evolved since the usenet days of the 1980's, along with our own little tweeks and refinements in recent years right here on TFF, has slowly homed in on a way to conduct the process with more reliability and efficiency.

Achieving a biofilter during fishless cycling that can process 5ppm ammonia in to zero ppm ammonia and zero ppm nitrite 12 hours after the 5ppm is dosed for a whole or at least partical "qualification week" is a really tough quality requirement. It may overshoot or undershoot the real needs in a few cases. But I feel it is our best effort at producing an excellent freshwater environment that new fish can be dropped in to and have the best chances of not only surviving but also thriving.

~~waterdrop~~