I know people who only achieved a .5 rise in pH it solely depends on how much alkalinity you go through a day, personally I would aim for a stable ph of 8.3 because if something happens like for some reason your dosing pump goes batty and dumps a ton of Kalk water in your tank you have some room if not and you stay in the high side you could potentially nuke your tank, a pH of 8.4 or 8.3 will not make much difference in coral growth. That is just my 2 cents.My tank is stocked with 7 large tangs and light is barely at 15%. The tank is also in a area with windows and close to the front door. Just for the hell of it I turned on my T5 and the PH went up to 8.28. Below is my open sump, i am sure this helps. However, my basement system PH is always on the lower side (8.0-8.1). If I can keep it above 8.3 naturally that would just make my life easier not to have to monitor if its too low.