a 135 is perfectly suitable for a russels lion as they are a bit smaller than a volitan a vol would be ok for some time but will eventually need to be upgraded to a larger tank if housed with many other large species ..try to avoid more aggressive species of fish such as trigger and some wrasses as they will tend to nip at lions fins also some eel species will also do this but not all..puffers and lions dont always do well in the same tank either as puffers are more of an agressive feeder .and lions do not compete well for foods .. if a lion is your first choice for fish stock be sure you have it eating well and adjust any newcommers to its compatability