Can I add another fish?

[Xj reefing]

Hi guys I just wanted to know if I could add another fish to my 20 gallon reef tank. In there currently there is 2 clowns who go everywhere, one blue spot blenny/peacock mudskipper who hides in the rocks now days and 1 purple fire fish who hangs out near the bottom at the back of the tank. Could I add a Bangai cardinal if I added a air stone and some more bio media. I have heaps of both already but it is better safe than sorry.

[aclman88]

What is your filtration like? Is this an all in one or a standard 20gallon? Are you running a skimmer? 

[Tired]

Air stones and biomedia don't matter. Amount of rock you have matters somewhat, since that's where all your biofiltration is. 

 

I would probably not put 5 small fish in a 20gal, especially since one of them is a decent-sized blenny. That being said, how often do you do water changes, and how high do your nitrates get before each water change? 

[Xj reefing]

I do water changes once per week and the nitrates are usually at 10ppm.

[Tired]

I should have also asked, are all your fish full size? If they are, and nitrates stay reasonable, then you could add something else. If not, you can't tell if something else would be OK, bioload-wise, until they're at least nearly full size. 

[Gourami Swami]

I wouldn't, it's not only about bioload (though that is a wise concern) but also territory and swimming space. If it were my tank I would leave it as-is.

[Matteo]

Nah you're pushing your load already

[Tired]

Yeah, I doubt the nitrates will stay as low once the fish are all adults. Assuming they're probably babies right now- especially the blenny. But "do the nitrates rise quickly" is a good way to check bioload, in general. 

[Edwardfish]

I would have to say no also unless It’s maybe a 20L skimmer and tons of bio media, that’s a pretty big blenny for the tank and clowns also have a large bio load especially when full grown, my lfs has two clowns I wouldn’t even put alone in anything smaller than 20.

[Xj reefing]

They are still babies so I might hold off until I get a bigger tank thanks for the help