STN ...frustrated and can't figure this one out!

[SteveDola]

and if you think your test kit is correct and youve had 7dkh for years (like me) then its not the low alk. MANY MANY successful stony keepers keep their alk at 7/8. In fact Ive had my alk drop to 5-5.5 without a massive STN event...did lose a couple (namely my oregon tort) but not an entire collection. Even if it drops to 6s youd be fine if you were starting form 7dkh. If you were starting at 10? then go to 5...Buuuuhbye stonies

 

[reefkeeper2]

I don't think it's the lower alk itself that might start the STN, but the resulting low nightime pH that can occur when your alk is running on the low side. I can get away with an alk of 7 in the summer when the windows are open, but in the winter with everything shut up and the furnace running ---STN. The pH dips just a bit too much at night and I think that's the trigger. If I boost the alk in the 8-9 range, it stops.

 

[SteveDola]

I have a feeling too that PH fluctuations maybe the cause of the stn events and thats kinda why I asked if he took his fuge off line. The change in skimmer may contribute to the oxygen levels in the tank and now at night the tank is just under the threshold that the corals can handle. It wont hurt to raise the alk to 8/8.5 Dkh slowly to see if that will help stop the necrosis.