how often? I normally do 30% twice a week
With small Cichla I do about 10% each day, they are sensitive for big waterchanges when small. Sometimes I will skip a day (or 2) without problems
When really small I put them in my guppy tank with 250-300 guppys, they are way to small to eat the adult guppy's but they will enjoy the new born ones and grow fast. Needless to say that the guppy's will have to be healthy!
When they are around 3-4 inches they move to a growout tank, and i feed them smelt (cut in smal pieces), bloodworms (frozen) and start pellet training them by throwing in some Hikari pellets.
Raised 15 cichla till now (3x 5) and haven't lost a single one
The Azuls I raised were 3 cm (1,2 inch) when I bought them, 7-8 weeks later they were around 14 cm (5,5 inch)