Well, it's a bigger tank and waterchanges are expensive on larger volumes of water like that. You really only perform REGULAR (not emergency) waterchanges for 3 reasons:
1- Out of control nutrients (can't handle nitrates/phosphates)
2- Replacing trace elements
3- Replacing calcium, alkalinity, and magnesium (if coral load is low)
If you can control nutrients well through skimming, refugia, sumps, or other means you can waterchange less frequently. For beginners with no hard corals like yourself and hardy softies, I'd suggest 30% every second week, or maybe even every 3rd week depending on your nutrients. Once you get more experienced, you can lengthen that period, but increase the magnitude of the change. I for example only waterchange to replace trace elements. My nutrients are held in check through vigorous skimming and refugia growth, and I use suppliments to maintain calcium, alkalinity, and magnesium. As such, I waterchange about 75% quarterly (4 times a year). Again, not reccomending you do this straight off the bat, but you can move towards that goal as you progress in the hobby.
