New Tank Water Conditions

Chlorine first as that's an easy one. Did you add a dechlorinator, and do you know if your water company uses chlorine or choramine to treat their water supply? Chlorine does gas off after about 24 hours but chloramine does not. If you have chloramine and did not use a dechlorinator, that could well be the source of your chlorine reading. However, it sounds as though you are using a strip tester and they are notoriously inaccurate. If you used a dechlorinator at the correct dosage when you filled the tank and use one to treat the new water at every water change, you can't have chlorine in the tank.

A lot of the bottled bacteria products contain the correct species of ammonia eating bacteria but the wrong nitrite eating bacteria. The Fluval product is not one of those allowed to use the correct species of nitrite eaters (use of the correct species is copyrighted or patented or whatever the term is, and Fluval can't use it).

Ignore any tester that says any reading above zero for ammonia and nitrite is OK. The only safe readings for them is zero.
The best way to keep nitrite (and ammonia if that does show up) under control is by water changes. You need to keep both of them below 0.25. The amount and frequency of water changes is determined by how high the readings are and how fast they got that high. You don't mention how big the tank is, but the larger the tank the longer it will take for the levels to rise because in a large tank they are diluted by the amount of water. if your nitrite test shows near the 0.5 colour, do a water change. You might find it easier to buy a liquid reagent nitrite tester as they are more accurate and the API one at least does have a colour for 0.25 (it sounds from what you say as though the tester you are using goes from 0 to 0.5)

Once your ammonia and nitrite levels stay at zero for a week without you needing to do a water change, you can get more fish if the tank is big enough - BUT only a few at a time. The rule of thumb is no more than one third of the fish you already have, so for you that is 2 guppy sized fish, or one fish twice the size of a guppy. Test daily after adding, and when you've had a week of zeros, you can get more fish.

Your water company may say on its website which of the two treatments they use, chlorine or chloramine. If it doesn't you can always email or phone them.

If you have chloramine, adding the stress coat will help, if you have chlorine it should have gassed of by now but still add the stress coat - dechorinator also remove metals from the water. Make sure you use it whenever you do a water change.
Unfortunately, chlorine/chloramine are added to the water supply to kill bacteria. As you didn't use a dechlorinator when you set the tank up you may have killed the bacteria in the supplement you added.


Six guppies in 110 litres is perfect for a fish-in cycle, which is what you are doing. Not enough fish to send the ammonia and nitrite levels rocketing, but enough for the cycle to proceed nicely. Keep monitoring those two and do water changes whenever they get near 0.25. And when you have grown enough bacteria for these 6 fish, take it slowly when you get more fish. As you have more fish, you'll be able to add more at once - the number of fish will be increasing so one third of them will be more 

I understand the nitrate cycle to be as follows:

Fish waste -> ammonia -> nitrites -> nitrates

Assuming I am correct, the fact that I have had two successive 0 ammonia tests would suggest the ammonia eating bacteria is present and any chlorine that was in the tank hasn't killed it. So I guess I am just waiting for nitrite eating bacteria to build up.

That is correct  It would indicate that the bottled bacteria did indeed contain live ammonia eaters (some brands contain dead ones!) but no viable nitrite eaters.

Water changes are the way to go. A 30% water change will reduce the nitrite level by a third so 0.4 would go down to 0.28. To make any serious impact, you have to do a bigger water change. A 50% change would drop the level from 0.4 to 0.2; a 75% water change would drop it to 0.1. I know big water changes are not done for fun - I have recently had to medicate my main tank and after 2 days do an 80% water change on a 180 litre tank, which took all morning. But once you get that reading down, frequent smaller water changes will stop it getting that high again.


It is OK to add 1.5 times the stated dose of dechlorinator, but I wouldn't go any higher. One way to dose a bucket is using a syringe. You can get them on-line quite easily or from a chemist shop - if you do this ask for a babies' medicine dosing syringe or you might get the third degree about why you want it if you ask for just a syringe. They come in sizes from 1ml to 10ml and it is easy to measure tenths of a ml using one.



You can always practice water changes using a bucket 

I rinse the test tubes, then rinse again and yet again. After letting the bulk of the rinse water drain out for a minute or so, I use a paper hanky to dry the tube. I hold the lid under running water, then drain briefly and dry. The danger comes from leaving any residue behind in the tube.

Swimming up and down the glass is common in new fish. It could be that they can't see the glass and until they learn there is a barrier there they try to swim though it then round it.
Lack of oxygen caused by lack of oxygen or the fish thinking there is low oxygen because of ammonia in the water shows quite distinctive behviour in fish. They hang at the surface and gulp air. It sounds as though your fish are swimming not just hanging. And of course guppies feed from the surface so they will congregate there if they have been fed or think food is coming.

Guppies are closely related to endlers, and my last two endlers have just died. Endler males display to females, or each other if there are no females. They spread their fins, arch their bodies sideways and sort of twitch in front of another fish. From your description it sounds as though your guppies are doing something similar, and if my desriptions sounds familiar, your guppies are displaying to each other since you don't have any females. Word of warning - they may also try to mate with each other, or with any other fish species you may add. Male guppies have one track minds!

Mature media will indeed help, even a tiny bit. It is getting the bacteria started that is the slowest part. Remove a bit of new media if necessary to get the old stuff in there.
It should be placed inside the new filter before the new media in the direction of water flow. Old media in physical contact with new will spread bacteria into the new media faster and it should be first in the water flow so that any loose bits of bacteria-containing biofilm get washed into the new media.

Your friend can lose up to a third of his media with no ill effects. The two thirds of the bacteria he has left will multiply quickly to make up the loss.



I think with guppies and endlers, there is also a bit of 'look at me, I'm better than you' so that should a female appear the 'best' one gets first chance with her.

To be honest, you could put it instead of your carbon pad. Though not just yet, you need every bacterium you have at the moment. In the meantime, between the carbon pad and the other pads is fine.


Can I ask, what exactly is in your filter? You mention a carbon pad and two other pads - what are they like? I ask because some filters put terrible media inside them. Most filter manufacturers use carbon, which isn't necessary, and some use zeolite which is ore than useless long term. Once you have grown a full set of bacteria you can tinker with the media till you get a good set.

I used to have a Juwel Rio 125 and although I did remove the filter I had it for a while (incredibly noisy pump; tried a new one and that was as bad. Kept us awake in the room above  )

The blue sponge is home for the bacteria. In my Rio I had both coarse and fine.
The green sponge is supposed to remove nitrate but doesn't. But it is a good home for the bacteria, treat it like a blue sponge.
Juwel say to change these sponges every few months. Don't. Wash them in water you've taken out during a water change. Squeeze them gently, don't try to make them look like new. When they go holey and shapeless, they do need changing but only one at a time. Or even better, cut them in half and change one bit at a time with at least a month between.

The white pad that goes on top gets clogged very quickly and loses it's shape after a couple of washes. It needs replacing very regularly; too regularly to grow many bacteria in the time it's there, and filter wool isn't particularly good at growing bacteria in the first place. Juwel white pads are expensive; buy a roll of filter wool and use a white pad as a template to cut the roll up.

The black sponge is impregnated with carbon, and in the Rio it was a lot thinner than the blue & green sponges. Wait until the tank is cycled with a full fish load then take it out. Either replace it with another blue sponge or leave the space empty in case you ever do need to use carbon to remove medication after the treatment has finished.

Provided you avoid the med that Sanjo had, the bacteria should be OK.

And yes, any tiny bit helps. It is possible you didn't have quite enough nitrite eaters and the mature media had enough to get to the optimum number.

I do understand your dilemma; I'm restocking after losing a lot of my fish and the loss of a lot of my filter bacteria due to reduced ammonia made by the lower fish numbers for the last couple of months.

Shoaling fish prefer a minimum of 6 rather than 4 despite what the fish profiles/community creator on here say. And some nippy species (you don't list any) do better with 10+ to keep the nippiness within the group.
The other annoying factor is that most shops sell shoaling fish at £x per fish and £y for 5.


The one third of fish already in the tank 'rule' is to prevent any ammonia or nitrite showing up after adding new fish. The filter bacteria can double in number in 24 hours under optimum conditions (though few tanks have these optimum conditions of pH, hardness, temperature etc).
If you are prepared to monitor your water conditions on a daily basis again, get a shoal of one of the species on your list. You will probably find a slight rise in ammonia as the new fish would make the same again as the guppies, but nitrite might well not show any increase - the ammonia eaters will grow slowly till there are enough of them to remove the new ammonia load, and they will increase the nitrite level slowly rather than all at once as for ammonia; the nitrite eaters should be able to keep up with the slowly rising nitrite level.

Once you have 12 fish, getting another 6 next time shouldn't have quite the same effect on the ammonia level, but still keep a eye on that and nitrite.

After adding one batch of fish, wait until you've had double zeros for a week before getting the next batch.

With 110 litres in the tank, even another half dozen fish shouldn't cause the ammonia level to get too high too quickly. As long as you do stick to just another half dozen fish you should be OK testing every couple of days. And if you do see ammonia, do a big water change to get it really low rather than a small one to get just below 0.25 so it will take longer to build up again.


Otos would need to wait a few months until the tank has grown a good supply of algae. The other types in your list should be OK whenever you want to get one as they will eat algae wafers, cucumber, courgette (which is more nutritious than cucumber) etc. Research the catfish on Seriously Fish and planetcatfish as some plecs need wood to graze on - though if you already have wood, that's fine.