If you are setting your 125 gallon up useing the Ecosystem method, which is a method of not using a skimmer, or carbon and using MACROALGAE'S and lots of LR for natural filtration IMO, You are doing a very good thing, I set my 75 up as just a normal tidepool, with carbon blah blah blah and a skimmer blah blah blah, I had nitrate problems, Ammonia, Nitrite, pH and alllll kinds of other problems, including head and lateral line desease with tangs...
then, about a year ago I put on a refugium, 15 gallons with LR, and Calurpa Algae in it and I have not had a problem with ANYTHING, my yellow tangs LL has completly healed and I have never been able to keep flowerpot corals or other hard corals before untill now, Now I have a THRIVING reef, with LPS, SOFTIES and SPS even a clam now, with NO PROBLEMS!!!!
The refugium method or Ecosystem method simulates nature in every way, it provids a deep sand bed for maximum denitrification and the calurpa algaes for consuming the wastes and using them to grow, it also provides a home for your pods and other critters so they make more of themselves, the larva of these critters travels up to the display as zooplankton and FEEDS YOUR CORALS!!!
That is why I believe that this method is the ONLY way to go!!!!
I have seen other people use this method and they all agree that they have had more success with this method than any other way they have set up a reef before!!!
also, I would do waterchanges like, once every other month of so to replace some elements in the water that maybe get too low, all you need to do other than feed your fish, add water, and watch is to buff your tank... then tada youve got yourself a healthy thriving ENVIRONMENT/ECOSYSTEM instead of a "fish tank"
, hope this helps, I STRONGLY ENCOURAGE YOU to do this, BELIEVE ME YOU WILL NOT BE DISSAPPOINTED, BTW: you can use your extra algae you grow to feed your herbivorous fishes!!
enjoy your ecosystem!!!