Very nice build. You did a great job organizing that closet. That will make an amazing looking sps tank. May I ask why you are using to use the bio balls?
I wanted to switch around the plumbing to give me the control at each one of the returns. Now each return also has a back flow valve on it.
I know that bio balls need to be cleaned, and can be a bit of a pain, I may end up taking them out, but for know i will continue to clean them monthly
my philosophy is to just regularly clean and maintain your prefilter, then the bioballs mainly house your bacteria instead of detritous and don't become a "nitrate factory". I clean my prefilter every week - 2 weeks.