High Nitrite And Nitrate Levels But 0 Ammonia

Hi, we are very new to keeping fish and would be grateful for some help. We were very naive and I realise now, quite ignorant in venturing into this. We have a 25l tropical aquarium and currently our Nitrite and Nitrate levels are very high but ammonia is showing as zero. We thought we had cycled the tank before we put the fish in but now I'm not sure if our tank is finished cycling. (we left the tank running for two/three weeks before adding fish and it's now been 4 weeks since we put the first fish in.) Having looked online the advice seems to be conflicting, some say partial water changes every day and add bacteria, what I assume they mean by this is stress zyme? Other advice I've had is to stop doing the partial changes and leave it be. Can anyone tell me what is the best thing to do? I'm worried that if the cycle is not complete that I'll stop it by doing partial changes but equally I don't want the fish to be stressed or die.

It does sound as though you are doing a fish-in cycle so you will need to do lots of water changes till you have zero nitrite as well. A tank is cycled when both ammonia and nitrite stay at zero. The highest safe-ish level of nitrite is 0.25, so if yours is above that I'm afraid you will need to do water changes. If it is very high, you need to do more than Colin's 8 litres to get it below 0.25 but once you've got it there the 8 litres twice a day will probably be enough to keep the reading low.

Very few bottled bacteria products do anything at all to help the tank cycle, I'm afraid. Even the few that are known to work don't work all the time as mishandling during transport and storage can kill the bacteria in the bottle. And Stress Zyme is not one of those that are known to work I'm afraid.

As Colin asks, what fish do you have and how many? High levels of ammonia and then nitrite are made worse when there are a lot of fish.

Very very few shops will tell you about fishless cycling. Mostly they are old school and say to just add fish, not bothering to tell you about the water changes or that they'll make more money when all your fish die. Or they will sell you bottled bacteria and omit to mention that most of them say to stock the tank slowly.
And it is all to common for shops to lie to make a sale. They should not have sold you all those fish for a 25 litre tank. Well, I suppose they could just be totally ignorant..... 


You should clean the gravel. There will be fish poo and uneaten fish food in there decomposing to make even more ammonia. If you haven't cleaned it yet, do some of it at the next water change. The mess will have mounted up (unless you have been doing gravel cleans) and you won't get round all of it at one go. Once it has all had a deep clean, next time you'll be able to do the whole lot in one go.
But don't touch the filter unless the flow from it is visibly slowing down. If you do need to clean it, squeeze/swoosh the media in the water you take out during a water change.

I'm afraid just the neons makes the tank overstocked. Adding the guppies pushed you to 200% stocked according to the community creator. And it depends on what the catfish is as to how much that adds to your stocking. A corydoras or otocinclus won't add much but the problem with them is they are shoaling fish and you'd need at least 6 of them. If it's a plec of some sort, there are none suitable for a tank your size I'm afraid. And they are poo machines 

To make this tank work, you could keep just the guppies. That would make it almost full. But you would need to rehome the neons and catfish. Or rehome the lot and get either 1 betta (siamese fighting fish) or 6 male endlers.

Oh, and I should ask, are the guppies males, females or a mixture? Guppies breed worse than rabbits which will only make the situation worse.

Just about the plec first. If it is a bristlenose you need a tank at least 60cm long x 30cm wide. If it is a common plec, you need a minimum of 120cm x 45cm. Common plecs grow huge.


Since you are already half way cycled, the simplest thing with a bigger tank would be to move everything into that - fish, water, decor, gravel (cleaned in the transfer) and the filter. The filter might be too small for a new tank in which case put all the media inside a new filter and use the media that comes with that to fill up the spaces. The media inside the filter you have now contains most of your ammonia eaters and probably some nitrite eaters. You just need to grow more of them. There will also be some bacteria on all the surfaces in the current tank but not nearly as many as in the filter. Moving the decor will transfer a few bacteria as well. The reason that most bacteria grow in the filter is that has a constant flow of water bringing them food and oxygen making it a desirable residence.


A 60 litre, 60cm long tank would be fine for the guppies and neons, but not the plec even if it is a bristlenose.
A 100 litre, 80cm long tank would be fine for the guppies, neons, a bristlenose and even a few more fish.
If it's a common plec, you'd need much, much bigger. They'd probably outgrow even that 120cm long tank that Seriously Fish recommends. To be blunt, if your plec is a common, I'd rehome it.

And you could use the 25 litre for a quarantine/hospital tank, or get a betta!

Thanks Sue, that's a great help and Colin, man after my own heart, doesn't everyone have their gravel on the top  ? Looks like I have a lot of reading and thinking to do. Thank you both, I'm hugely grateful for your support.

oooo - just as an after-thought. Guppies need hard water and neons need soft water.... d'you know what the hardness of your water is? You can find out from your water suppliers web-site. They will have a page where you can put in your postcode and it will give you a run-down of your water quality.

Thanks Colin for the extra info, I'll check that out. 

Thank you Fishcake76, you're very kind, and thanks too for the advice. 

It's great to know you are all there to call on for help and to share with. Thanks.

Looks good!

I knew it was too good to be true, one of the guppies died overnight    I guess given all they have been through it was only to be expected.

As for the filter FC72, the air tube is noisy,  I don't know what the answer is to this. Sorry.

Thanks FC, your tank looks great, thanks for sharing. I hope the new additions are settling in.