in crowntail bettas ot can cause very noticable fin curlong and not as noticable and severe fin curling in other betta types, this will not effect the Betta negatively at all.
Elevate amounts of leaves will naturally soften the water, aswell as most types of driftwood, this will also realease beneficial tannins with very positive effects, they are known to help prevent diseases, make the fish feel better, and with leaves, provide a place for males to nest (under them)m the water will turn slightly brown though depending on the amount you have and whether or not you use carbon. Another way would be to add a small amount of peat moss to the filter
It only becomes a problem of you have certain fish that are sensitive to relatively hard, and the exact parameters, usually amazon river based fish thrive in softer water and can't handle very hard water without being very succeptable to diseases and having there life span shortened, depending on your exact parameters your Betta should typically be completely fine as they are very adaptable fish and can thrive in a wide range of water hardness and PH's
Last edited by Mo; 05-04-2012 at 07:21 PM.