Newbie Fishless Cycling Question

[BlueIn2Red]

Hi guys,

I’m currently fishless cycling my first aquarium, a 100 litre tropical tank. I thought my thousands of hours of research was enough, but apparently not, so please read on!

The tank is quite heavily planted, and the plants are doing well. I have been water testing daily and feeding Dr Tim’s ammonia as necessary. I also added some API QuikStart at the beginning, and have added a bit more after one week. I am just over two weeks in so far, and the tank has reached what to me seems like a strange equilibrium - I can “feed” 5ml of ammonia one day (resulting in a test reading of 4ppm), and the next day the ammonia level will be zero (so presumably the good bacteria are doing their thing), nitrates will be zero (I assume consumed by the plants?), but nitrites are consistently at 2ppm. I have done no water changes so far, only a couple of small evaporation top ups.

Obviously I need to get the nitrite level lower. Do I just need to wait to give the bacteria more time to grow? I’m a little confused that nitrites aren’t turning to nitrates, or perhaps they are and the plants are consuming the nitrates before I can get a test reading? I am not in any rush to add fish, but want to be sure I’m doing the right things in the meantime.

Thanks in advance!

[Colin_T]

Hi and welcome to the forum

If you have a lot of true aquatic plants that are getting lots of light, they will be using a lot of the ammonia and possibly some nitrate.

If you have a heavily planted tank, it is very hard to do a fishless cycle because the plants use most of the ammonia and inhibit the beneficial bacteria growth.

If you do have lots of plants, I would drain and refill the tank with dechlorinated water, wait a week then add some fish (assuming there is no ammonia or nitrite, and the nitrate is less than 20ppm).

[Aiken Drum]

In a cycled tank, you would expect 4ppm of ammonia to come out as around 11ppm nitrite, and that nitrite to come out as around 14ppm nitrate.

Some of the ammonia and nitrate will be going into the plants, so these numbers can be lower. How much lower will largely be down to what plants. Even a large number of slow growing aquatic plants will have negligible effect on your water parameters. A small amount of fast growing surface plants could remove everything.

You have only been going at it a couple of weeks, a couple of months is more typical to cycle a tank. The nitrite to nitrate stage usually takes longer than the ammonia to nitrite stage.

Cut back on the ammonia, 2ppm is more than enough to cycle the tank, will produce less nitrite and you may see more clear results of nitrite dropping quicker if not so much is being produced. Give it a little more patience.

[BlueIn2Red]

Ok, thanks guys. I’ll take Aiken’s advice for now as it seems a little less drastic than almost starting again. I’m in absolutely no rush to add fish, enjoying the planted tank as it is already. Just wanted to make sure it was simply a matter of time rather than something going wrong.

(I have no surface plants yet btw.)

[BlueIn2Red]

Forgot to say, I was adding 5ml of ammonia (to get to 4ppm) because I was getting a zero ammonia reading within 24 hours, which I took to mean that the good bacteria had “eaten” it all, and that I should continue at (at least) this level to ensure they have enough to feed on while there are no other ammonia sources (i.e. fish). Is that not reasonable logic? If I add half as much, won’t there be a danger of starving the good bacteria and losing some?

[BlueIn2Red]

Here’s a picture from a couple of days ago to show the planting level etc:

[BlueIn2Red]

Today I got a 10pm nitrate reading btw, to go with the usual 0 ammonia and 2ppm nitrite. This makes a little more sense to me!

[Aiken Drum]

Originally Posted by BlueIn2Red

Forgot to say, I was adding 5ml of ammonia (to get to 4ppm) because I was getting a zero ammonia reading within 24 hours, which I took to mean that the good bacteria had “eaten” it all, and that I should continue at (at least) this level to ensure they have enough to feed on while there are no other ammonia sources (i.e. fish). Is that not reasonable logic? If I add half as much, won’t there be a danger of starving the good bacteria and losing some?

A fully stocked tank will be putting the equivalent of maybe 0.5 to 1ppm ammonia into the water in 24 hours. Nowhere near the amount you are dosing. The microbes removing ammonia will grow or die back depending on the amount of food available, but will do this over months not days. Cutting ammonia from 4ppm to 2ppm wont make any difference to what you have built up so far, but will reduce the amount of nitrite going into the tank and reduce the time it takes to cycle out the nitrite. You dont need that 10ppm nitrite to get the nitrite to nitrate stage going. You dont want it getting too high, if it goes beyond the ability of your test kit to read, water change to bring it down to readable levels.

[BlueIn2Red]

Understood, thanks again.

[Colin_T]

The tank looks good but a couple of things. I'm not sure if there is a picture on the back of the tank. If there isn't, then add one to help the fish feel more secure (when you get fish).

The rock that runs across part of the tank could hide bodies and uneaten food behind it. Make sure you can see behind any objects in the tank and clean behind them each week. Same deal with the driftwood.

If you get fish that jump, make sure you have a coverglass on the top of the tank. Coverglass will let light in but stop fish getting out. It also helps trap heat and reduces power consumption and reduces evaporation.

[BlueIn2Red]

Thanks. It’s a terrible picture but it does have a lid, and the rock formation is a kind of wall with substrate filled in behind it, so no hiding places as such.

[BlueRosenBloom]

Originally Posted by BlueIn2Red

Here’s a picture from a couple of days ago to show the planting level etc:

Oh the tank looks lovely, can't wait to see fish in it!

[BlueIn2Red]

Update: nitrites at zero today for the first time since the tank was started. Nitrates still present and up there at 40ppm though, which I’m taking to be a good sign (i.e. nitrite conversion process is underway). I’ll keep an eye on that nitrate level in the coming days - I’m assuming the plants will bring it down, but if not I’ll do a water change.

(If any of this logic is wrong, please shout!)

[Aiken Drum]

How long did it take between dosing 2ppm ammonia and seeing zero ammonia and nitrite?

[BlueIn2Red]

48 hours (possibly less, I wasn’t able to test yesterday).

[Aiken Drum]

If ammonia is below 1ppm then redose it back up to 2ppm. When you are able to dose ammonia to 2ppm and 24 hours later your ammonia and nitrite are both zero you are cycled sufficiently to moderately stock your tank.

[BlueIn2Red]

Right, I think I’m close, because ammonia is zero also. Isn’t the nitrate level too high still though? I plan to start with six neon tetras btw.

(I dosed 2ml of ammonia today, fully expect that to be zero tomorrow, but not so sure about nitrites, as today was the first time they’d reached zero.)

[BlueIn2Red]

My tap water nitrate level is 10ppm incidentally.

[Aiken Drum]

Do a big water change to bring nitrate down to about 10ppm before adding fish.

Dont expect the nitrate to just get lower on its own. While plants will use nitrate, from your photo there doesn't appear anything in there that will make a measurable difference. When you add fish the nitrogen cycle will likely produce nitrate at a much quicker rate than plants will consume it as well. If the plants are consuming nitrate at a quicker rate than plant uptake you should look at fertiliser that contains nitrogen (most dont) to keep it at a good level for plants.

[BlueIn2Red]

Zero ammonia and nitrites today, so I think I’m essentially cycled. Nitrates still at 40ppm (maybe a tad less, hard to be sure with the test colours) as expected. I think I’ll not add ammonia today and test again tomorrow just to make sure things are stable, then do a 50% water change tomorrow and test again the following day. If then zero ammonia and nitrites, and low nitrates (10-20ppm), then I’ll add my six Tetras