acros bleaching after lowering alk

[CTaylor]

Hi,
My tank was doing very well. Except one acro started bleaching (from bottom up) about 1 month ago. I'll give details after, but in brief: My tank was doing well, acros and all. One was bleaching from the bottom. I lowered my alk from 10 ish to 7-7.7 over course of a week. Now try to keep it there. B/C my nitrates and phosph test a 0 with low scale tests.

Since I lowered my alk, one other bleached and died. Another one today started (bottom up) and will be dead soon (how it goes). However, those two acros I happened to have moved from one spot to another. The differences in par were 30 at most. One got 30 more, the other 30 less. But neither showed worse coloring. "just" the bleaching.

Is it possible that I actually need to keep my tank at 10 alk? Natural sea is closer to 7. And my nutrient level is (too) low. I feed pretty well (mainly b/c of my blue throat trigger in a 110 gallon tank). I feed 1/4 tsp reefroids most night to boost nutirent load. I have caheto, but even before I did, my nit and phoph were ~0.

I'm thinking to keep my tank at 7+, and that my two corals that just died or dying happened to get used to the 10 alk. So putting it back to 10 may just hurt MY tank in the long rung (I say MY tank b/c I know each tank is different, mine has too 'few' nutrients). Though a little voice in my head is saying to put it back at 10, so i dont know what to do.

BTW my lighting is 270 par on the bottom, where I keep my corals when I get them for first several weeks. Most actually look great down there (acros). It's AP 700 and a kessl a360 on either side << to give more even light.

Thanks!

 

[ca1ore]

Are the polyps bleaching or dying .... it's not the same thing. STN from the base up is usually dying. My experience with modest alk shifts is that they are only fatal if the corals were already stressed.

 

[CTaylor]

The acros may be stressed by the ~0 phos and nitrate . I have hanna ppBilion test for phosph - it reads 0. Low range nitrate RedSea reef test also reads 0 (clear in color). SO that could be a stressor (?). I guess it's stn, but it's not flaking off. Its just turning to white skeleton.
Can super low nutrients like NO3 and PO4 somehow be balanced with something like 'over feeding' of something like reef roids at night (when PE is most)?
Also my tank is "new" set up sept last year. But everything was doing really well (possibly adapted to my off kilter levels.
Thanks

 

[rvareef]

post some pics of the corals and tank

 

[Tripod1404]

The acros may be stressed by the ~0 phos and nitrate . I have hanna ppBilion test for phosph - it reads 0. Low range nitrate RedSea reef test also reads 0 (clear in color). SO that could be a stressor (?). I guess it's stn, but it's not flaking off. Its just turning to white skeleton.
Can super low nutrients like NO3 and PO4 somehow be balanced with something like 'over feeding' of something like reef roids at night (when PE is most)?
Also my tank is "new" set up sept last year. But everything was doing really well (possibly adapted to my off kilter levels.
Thanks

I think your issue is very low nutrients like you suspect. Do you use GFO?.

Imo over feeding do not work for increasing nitrate, it can increase phosphate for a short period after feeding but at least in my case, it drops back to ~0 in few hours.