Strange Die Off!

[Reefer525XL]

What can cause a frag to completely vanish overnight? To my knowledge all Parameters are in check and I would like to think there are no bugs in the tank since I always dip everything using bayer but theres always a possibility.

Over the past few weeks randomly a frag that has been in the tank for weeks to months just sheds all its flesh overnight. I always check my tank before going to bed and these frags that have died look perfectly okay and in the morning boom, they are gone.

Tank is a year and six months old. Below you can find the level of the parameters I test for.

Ammonia: 0 (API)
Nitrites: 0 (API)
Nitrates: 0 (salifert)
pH: 8-8.2 (Apex)
PO4: .01 (Hanna)
Alk: 9.3 (Hanna)
Cal: 490-500 (Salifert)
Mag: 1440 (Salifert)

The whole systems with main display, sump and frag tank is a little over 400 gallons. I do weekly water changes (45g) and dose AcroPower once a week (100ml)

 

[NeilFox]

If those are your real numbers and your N3 and PO4 are that low you need to drop your Alk some perhaps. What else are you doing? Are you using GFO or dosing carbon?

 

[Potatohead]

I've had this happen twice also, including last night. I can't really explain it because everything else looks fine. I've heard that SPS will sometimes simply die for no apparent reason, it seems maybe to be true.

 

[Reefer525XL]

If those are your real numbers and your N3 and PO4 are that low you need to drop your Alk some perhaps. What else are you doing? Are you using GFO or dosing carbon?

Yes those are my real numbers, I don't run GFO or dose carbon. Only method of nutrient export is skimmer and refugium filled with chaeto.

I've been doing some ready and yes it seems that for low nutrients alk needs to be at or below 8.

 

[Reefer525XL]

I've had this happen twice also, including last night. I can't really explain it because everything else looks fine. I've heard that SPS will sometimes simply die for no apparent reason, it seems maybe to be true.

Have you tested nitrates, phosphate and alk? No that I think about it most of this strange die off began happening as I increases alk levels. Used to be at around 7.8 and I slowly increased it to to 9 over a few weeks.

 

[Hentz]

I run ZEOvit, aka ultra low nutrients. I have found if my alk dips below 7.5, my corals start looking dull and they retract their polyps a tad.
I've found my tanks sweet spot at 8.3