Hi I suggest you visit my website and pay particular attention to the Care and Maintenance article in the Articles section of the site, it will give you the essential information you need to know.
BRC.moonfruit.com
To sum up - 3 Bolivians in a 20 gallon is a bad idea, they are not harem breeders, you will end up with one pair and one rejected fish that will not last long.
The best way to select your stock is to start with a few - ie 10 juveniles as this allows you to properly select your prime males and females from the group as they mature - fish naturally mature at slightly different rates and so you will inevitably get late bloomers, you would be lucky to catch these late bloomers if you simply relied on pot luck pair buying in the fish store. One of those late bloomers may turn out to be the superior fish in terms of genetics, vitality, virility etc. I know a couple of mine were.
So what I did was to start off with 10 juveniles in a 15 gallon tank (I rescued them from the LFS as they were far too young to be sold) and I removed one or two each month as they grew, they were probably only a few months old.
After 2 months I had 8 larger fish left, so I moved them into a 20 gallon. All the time you are watching the fish and studying their behaviour, most times you will come to learn the males and females during this period, long before they hit sexual maturity (and therefore before you can accurately vent them). You can also get a very good idea of who the superior fish are. The site I referred you to at the start of the post also has a Sexing Guide to help with this.
Again the whole aim is to remove one or two of the weaker/inferior individuals every so often, after 4 months I was left with my group of 5 - 1 choice male and his 4 healthiest and favourite females. I had moved the final 8 to a 40 gallon once they'd grown out of the 20 and completed the final removal of the last two "inferior" fish, nothing wrong with them and they were re homed, not culled, but they were simply not as prolific as my others and so would have been constantly stressed in attempt to keep up with the breeding rate of the others etc.
If you read the care and maintenance article then you'll see that in a 30 gallon tank it is quite reasonable to keep 1m and 4f or 2m and 3f Bolivians full term, however in a 20 gallon tank you are limited to a pair of mature Bolivians.
The method outlined above solves the potluck fish store sexing method, trust me, they're really easy to sex once you get your eye in and learn the little give-away signs, it just takes a bit of time and experience first hand to really grasp it.
If it's impossible for you to get a larger number of fish and wean out then I suggest you do your best to determine sex, get your pair and contact me with photographs of each one, clearly showing a side profile of the whole fish (and at a decent resolution), 9/10 times I will then be able to sex it for you.
HTH
Blair.
this is what i have atm.
