I do pretty much do a min of 50% daily water change on a 280g and have yet to have any problems i don't think large water changes affect to much unless there is a big sway in ph which their shouldnt be unless you're tinkering with the water. With filter's it's always best to have two and clean one at a time, if you only have one you can still give it a really good clean just in tank water so you dont affect the bacteriea.
must take you ages!!!!but I imagine you get great growth!!
sorry to hear about the severum snowflake hope he recovers