3 mates for one Betta in a 5 gal?

[Quills]

I have a very happy Betta who is currently living with a ghost shrimp. The tank is very heavily planted. The top is slightly (about 25%) covered by 3 floating Anacharis. On the bottom I have one java fern and 5 more Anacharis that reach all the way to the top also. And I have 2 moss balls.
I am planning to go out and buy java moss and cover the whole bed with it. My filter is also contains all 3 stages of filtering (Mechanical, chemical and biological), and I have aeration and co2 feeding system too. The tank is fully cycled with ammonia at 0, nitrite at 0.3 (the nutrafin test says that 0.3 is good, I am unsure what that 0.3 stands for anyways), and pH at 7.1
Once the java moss covers the whole bed and works out, I intend to add a platy and cherry shrimp. Would that be a good idea? It's just I see how awesomely my Betta and shrimp like to race between all my Anacharis that I want to see a few more swimming too.

[Bombalurina]

Whilst the shrimp are fine (you could have as many as ten no problem) the platy is not a good idea at all. Platys are active fish that need a minimum of ten gallons. They are also social, preferring to be in groups of 3+, which your tank could not support. Finally, they are brightly coloured and boisterous, so could cause problems with your betta, especially in a small space.

If you have a nitrite reading, the tank is not cycled, by the way. Cycled would give you a reading of no nitrite and some nitrates.

[Quills]

So what kind of fish would you recommend that I could shove in there? I really want one more fish that I can fit in. Also my nitrite has been at 0.3 for about 4 months now. What kind of test do you use? Is it also nutrafin?
Also I got my platy info from here. Is it wrong? http://www.aquaticcommunity.com/livebearer/platy.php

[Bombalurina]

Hrm. Normally that website gives better advice than that. It's a sad lonely platy that lives by itself in a 5 gal.

I use AquaOne or API liquid test kits. I didn't like Nutrafin when I used them. The nitrite reading is part of the cycle - as you are doing it with a fish in the tank, you are likely to have a nitrite reading for a while. I would try upping water changes to reduce it.

There really aren't any other fish you should have in a 5 gallon, for three reasons:
- unless it is a very long, shallow tank, like the Petco Bookshelf, its footprint is too small to allow an active fish room for activity
- unless you have plenty of plants to support your filter, the tank will not cope well with the bioload, especially if you are still getting nitrite readings
- a betta is unlikely to enjoy sharing such limited space with another fish

Basically, if you want more fish, you need a bigger tank.