Welcome to the site! When u say u have a 30 gal filter, do u mean a an extra tank or a filter rated for 30 gallons? O and neon tertras need a small school of 6 or more, and i think that is probably the case with lamp-eyes as well.
they say its 1 inch per gallon, but if u do small schooling fish u could 2 inches per gallon, and for larger fish 3-4 inches per gallon. the phrase "u can't possibly keep a 10-inch pleco in a 10 gallon tank, but u can keep definatly keep more than 5 cardinal tetras in a 10-gallon tank." is commonly used to discuss this factor.
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