Help: Confused re: tank cycle

[thedoctor]

Problem:

I'm confused about my water parameters.

I have been doing fish-in cycling with 2 danios in a 100L tank (learnt about fishless cycling after LFS told me it was safe to add fish straight away...)

The tank is 100L, and has been set up for about a month now. I kept up my water changes as required to keep my ammonia at or below 0.25, and nitrites at or below 0.25 as to not harm the fish (as I have seen advised on the internet). All was going well, I had been getting constant nitrite readings (trying to keep at or below 0.25) with no-to-low ammonia and minimal nitrates (1-3ppm) for a week or two, when a few days ago I got a big nitrite spike to 1-2ppm. I did a big water change, dosed extra Prime, rechecked the nitrite and it was just below 0.25ppm. Then the next day, unexpectedly, the levels were: ammonia 0 (or very low - I have difficulty differentiating the colours), nitrite 0, nitrate 0. They have stayed this way for the past 3 days.

My question is - can my tank be fully cycled when I never got significant nitrate readings? The biggest nitrate reading I ever got was maybe 4-5ppm.

My tank is at ~25 degrees.

I have several plants including anubias, ferns, and amazon swords.

It gets about 10 hours of light a day.

I dose Prime as required, as well as Flourish excel and comprehensive

I feed NLS thera-a as per what fish eat in 1-2 min, 1-2x per day.

The filter is internal (combination of mechanical, chemical and biological)

Thank you in advance!

[smicko]

If you do waterchanges during the cycle the tank won't completely cycle so everytime you increase the bioload by adding fish or feeding more the tank will mini cycle.

The ammonia created by 2 danios wouldn't be nearly enough to cycle a tank that size, most of the ammonia would have come from the food.

You also won't get much nitrate as there will be very little good bacteria.

If you want to add more fish only add one or two at a time.

It would be helpful to know what filtration media your using as some are better than others. If you plan on having a fully stocked tank long term you would be better off with a cannister filter for bio media and use the internal for mechanical, aeration and water movement.

The plants will also use some of the nitrate so having such low levels would be considered normal for the situation.

Cheers mick

[Netto14]

So keeping in mind what [MENTION=885]smicko[/MENTION] said above a canister filter is the go.

Keep in mind every time you change water, plants or add a fish (and in the start up stages I'd only add one at a time) it changes the stage of the cycle all over again.

[Delapool]

Out of interest how much of a change would we be looking at here. I'd expect the tank to cycle as long as there is a source of ammonia (and I guess nitrite). But possibly water changes would slow down the cycling (to whatever ammonia level)? Just curious, not quite sure I caught the gist of it.

[PeterH]

Water changes will reduce the amount of ammonia in the tank. This will affect the number of bacteria that exist to deal with the ammonia - possibly reducing them as there is less food for them. Allowing it to build up will allow a greater population of bacteria which will deal with an increase of fish. At least, that's my understanding.

[Donny@ageofaquariums]

I would stress test it.... as in increase feeding for 2 days and then test. Sounds like you could add more fish tho.

In essence cycling is just slowly adding more food as the filter microbes increase in population and can process more.

[Delapool]

Thanks for the reply. My understanding is still in progress (although interested in why some tanks seem to cycle faster than others). Tanks here are all cycled so I'm just curious.

So reading through the posts I'm getting the impression that water changes are seen as a "bad thing" for fish-in cycling? Assuming I got that correct, then I'm a little confused as to why and look forward to further explanation.

My thoughts would be that as long as some ammonia is present (ie above 0), then the nitrifying population will still be building up to "catch-up". Here, I'm assuming that the population doesn't recognize say 0.5ppm or 5ppm ammonia as any different - it just means that there is more ammonia then the existing population can handle and they can increase.

So you could water change and keep the ammonia at say 0.25 (or say 0.5 if you don't trust the test kit / have lower ph and temperature). In the early stages you might be doing a 50% water change every other day, however as the bacteria population increases to match the ammonia food source, the need for water changes would get less as the bacteria population builds to match the ammonia level.

So I could see water changes slowing the cycle down (possibly) but not preventing it from completely cycling and the bacteria would build to match the ammonia level. This is in my own tanks where during cycling / mini-cycles I've always been battling to get the ammonia down and having a 0 reading DURING cycling has never been a problem.

Adding more fish would result in the bacterial population increasing again. (I'm not sure decreasing fish stocking would decrease the bacteria population straight away - I suspect some would go dormant).

[Donny@ageofaquariums]

Water changes during the cycle period are fine when you have fish in there because the fish will quickly produce more waste. Aint no bugs gonna starve yo

[The Tech Den]

I do not mind this article for a bit of a read.

Nitrifying Bacteria Facts

[smicko]

By doing waterchanges you reduce the amount of ammonia which means that you don't need as much bacteria to handle it. It just means you need to add stock more slowly than if you let the tank cycle without waterchanges, it is one of the disadvantages of fish in cycling. As Donny mentioned stress testing the system will be a good start to get bacteria levels up. If the ammonia stays low enough then let the cycle catch up then throw more fish in, even adding more food will create the ammonia needed to test the system.

Cheers mick

[Donny@ageofaquariums]

Yep thats about the sum of it. Basically we slowly increase the amount of food as the bacteria colony increases its ability to handle it.

Even when you add new fish, you dont add heaps more food. Just a tiny amount more than day before. Slowly increase over a week or so. It takes a week or so for microbe colony to increase in response to more food..... and we want it in balance.

[thedoctor]

Thank you all for your replies!

I will try to "stress" the cycle a bit to see what happens

[Delapool]

I do not mind this article for a bit of a read. Nitrifying Bacteria Facts

It's a nice paper although 'Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. At this pH almost all of the ammonia present in the water will be in the mildly toxic, ionized NH3+state.'... wish that would get fixed.

[Delapool]

Interesting discussion!

By doing waterchanges you reduce the amount of ammonia which means that you don't need as much bacteria to handle it.

Makes sense in total as say dose 4ppm and then water change brings it down to 2ppm for fish-less cycling. However, fish-in would still be adding ammonia. With say 10 fish in tank, the tank cycles to that level – water changes or not I would have thought.

By doing waterchanges you reduce the amount of ammonia which means that you don't need as much bacteria to handle it. It just means you need to add stock more slowly than if you let the tank cycle without waterchanges, it is one of the disadvantages of fish in cycling.

Kind of missing why the need would be to stock more slowly. The bacteria gets to the level of ammonia produced by say 10 fish and then you could add another 10 fish say. I’m not getting why I would fish-in cycle without water changes. Help appreciated!

[smicko]

I use pure ammonia for cycling if i need to cycle a tank these days, i don't do waterchanges at all. It adds the entire bioload the tank will have once fully stocked so by the time it's cycled you have to add fish so there isn't a die off of bacteria.

If you double the bioload of a tank it takes time for the bacteria to multiply enough to handle the increased bioload.

In this instance we are talking about a tank that has 2 danios if you add another 20 fish or even 2 fish double the size there will still be a period of time when the bacteria can't handle the increased ammonia produced so you would have to keep an eye on the level and if it gets near a toxic level you would do small waterchanges to save the fish from exposure, by doing the waterchange the cycle takes longer as the bacteria has to catch up to the total bioload.

Cheers mick

[Delapool]

Many thanks for the reply back and posted information.