Originally Posted by Rex Grigg
The 1" per gallon rule works quite well with most 1" fish. Beyond that point it's worthless IMHO.
Agreed, you could get away with 30 neons, otos, whiteclouds, cherry barbs, etc., but 4-5 full-grown angelfish would poison the tank (despite being less than 20 cumulative inches). The inch per gallon rule should be thrown out....completely out, IMO. The proper strategy would be grams/ounces (weight) of fish per gallon. It still wouldn't be foolproof, but it would be a lot better than the inch rule.
You did well to start with questions before you stocked rather than questions about why your fish are dying after...
I realize that your budget might not be too large, but a low-maintenance plant or two in your tank will go a long way towards keeping your fish healthy. Possibly some floating coontail (hornwort) or valisneria?
Also, run a search on the "nitrogen cycle" (ammonia/ammonium, nitrite, nitrate). If you are unfamiliar with this, you'll need to get to know it. Not that you need to understand all the chemistry, just know about the cycle. Without it, almost any fish tank would be doomed, so it will be worth your time.