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5 fish in 90 litre tank?


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I have 2 clowns, 1 chromis, 1 bicolor blenny and wanted to get a sixline next.


These fish have been there for 2 months and so far i have undetectable nitrates and phosphates.


Probably due to algae and having an oversized skimmer (rated for 300 litres)


It is ok to get a sixline on top of what i have?

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You are already overstocked and sixlines can be very aggressive and territorial. I certainly wouldn't add a sixline without getting rid of both the blenny and chromis. Plus, you've only had them for 2 months and unless you specifically paid for fully grown fish, they are all teeeeeny tiny compared to how big they get. While you may not have problems now, you certainly will as they get bigger - the amount food a fish consumes and the amount of waste they produce doesn't scale linearly with their size. By that I mean a fish doubling in size doesn't just double the biomass of fish in your aquarium, it actually adds 8x the biomass due to the square-cube law.


Juvenile fish only produce a fraction of the waste, require far less territory than, and are generally far more peaceful than an adult fish. Adding a small sixline now probably wouldn't be an issue for a bit, but the more time goes on the more unsustainable it'll be.


You also want to get your N and P up - keeping them at zero your tank is a ticking timebomb for dinos and/or chrysophytes.

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Yes i know that, i did already fight dinos. The tank has been up since 4+ months ago, the fish 2+.


Techically i dont have "detectable" n & p but i do have a lot of algae that might be consuming all the waste on top of the skimmer.


The reason i wanted a sixline is because i have some flatworms 


I thought the limit for a 23g tank was 5 😕


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1 hour ago, Entranced said:

I thought the limit for a 23g tank was 5 😕

There is no "rule" for number of fish per gallon since different fish have wildly differing requirements in terms of size, diet, territory, aggression and a million other factors - not to mention the dimensions of your tank play an extremely important factor. It's totally possible to have 5 fish (or even more) in a 20g if you were choosing tiny fish and scaped appropriately for their territorial requirements. It's also totally possible to have a 20g tank where you can't have more than a single fish.


If your 20g tank were an ~18" cube, you may even have issues with your chromis once your two clowns are fully grown adults if they start breeding. If they stake out the dead middle of the tank as their territory, they are going to see the entire tank as their territory and mercilessly attack (and kill) any openly swimming peaceful fish. Clowns can be extremely aggressive to anything in their territory (including you - fully grown they easily draw blood) and can smack down fish several times their size.


1 hour ago, Entranced said:

The reason i wanted a sixline is because i have some flatworms 

Buying a fish in a nano to deal with a pest is never a good idea. Depending on the flatworms you have, they may simply vanish in a few weeks and never return - they may just be one of the many populations that boom and bust in the ecological succession going on in your new tank. Have you ID'd the flatworms yet?

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