7 they grow to 2" so that would be 12 which gives them enoght room to swim
they like a ph of 6-6.8
if you need any more help im here!!
1 inch per gallon they r small fish so they won't produce alot of waste my nickname for them would be runny nosed tetras as they look like they have a cold and a runny nos
I have a Rio 125 (litre / 33 Gal) which is approx 3" long and I wouldn't want keep them in anything shorter they can really move when they want to.
It's a shame as their schoaling is fantastic, always together in a tight little group!
Also rummys are quite sensitive, you need fairly soft water in good condition, also if you do decide to get some take care bringing them home as they really don't like being moved... ...apparently they are know in the trade as 'crummy noses' because sooo many are lost in transit!
Once settled in though they are fantastic fish.
Althought I (personally) think your tank is a little small, if you do decide to get some you need at least 6 as they will be timid and suffer (no event alcimatise even) in very small numbers... ...they are a very timid, peacful fish... ...possbily my favourate!
Yes, neons would fit. Are you planning on having just the neons in there, or other fish too? You could probably get away with 10-15 neons, without any other fish.