good luck. hope you can get a bigger tank ... that may be your long term solution.
In the meantime - about the % of water changes - look at it like this: all of their waste and food waste is in their environment. the cleaner the water the more pleasant and healthy
as long as you're doing a water change, why not just change a little more? nothing hurt and I'm sure your fishies - that you obviously care about very much - would appreciate it.
again - good luck. I hope they stay mellow for you
30 g FW planted:corys, ABNP, blue angel, harleys, zebra danios, pair kribs, & nerite snails
15 g FW planted: crown tail betta, neons, snails
90 g FW semi planted: EBJD, congos, apple snails
90 Gal Journal: http://www.aquaticcommunity.com/aqua...ad.php?t=93939
Fishless cycling: http://www.aquaticcommunity.com/aqua...ead.php?t=5640
Cycling with fish: http://www.aquaticcommunity.com/aqua...ad.php?t=36492