PE is polyp extension, which is usually a good sign that your coral is happy, and looking for food. For a millipora, that means they look hairy and less stick like. For water changes I do 5 gallons of 0TDS RO/DI water every other day. Live rock from old tank would have a bit of die-off, but because I ran an ultra-low nutrient system (aggressive use of hi-cap GFO), the rock would be almost 0 PPM of phosphate, so no bad algae would grow off it, and almost a 0% chance of a HA bloom. The bit of HA I did get was from rock I bought second hand, and obviously had a bit of phosphate in it. Lastly, DI resin is De-ionizing resin, which brings the water coming from your Reverse Osmosis system from say 10 ppm (parts per million) of "unknown" particles, down to 0 parts per million, meaning the water I put in the tank is 100% free of any kind of contaminants of any kind. I understand that drinking 0PPM water would eventually kill you, as there is nothing in there for the body to absorb (salt, minerals, etc). Basically the only thing you are putting in your tank is the salt mix. No heavy metals \m/ or anything. Basically to have happy sps coral, I want almost nothing extra int he tank. Aggressive skimming, lots of substrate, and of course carbon and GFO running all the time. I also run a pellet reactor, that feeds bacteria that further cleans the water.