Acropora STN in tank with low salinity (30ppt)

[dtruitt]

I made the rookie mistake of calibrating my refractometer using RODI, checked against LFS water to confirm no egregious slope errors.

Refractometer is the red sea unit. I've been reading up on it and seeing that it's incredibly finicky and prone to giving vastly different readings on the same sample tested minutes apart.

After calibrating and improving my testing methodology, the tanks salinity appears to be around 30ppt.

LPS corals and Montipora are fine. A couple of acros that have been in the tank a while are looking okay, but newer acros are slowly receding from the base up.

I've calculated that topping off for evaporation with 10 gallons of water at 35ppt should bring the salinity back in check. This should take between one and two weeks depending on humidity and how low we keep the air.

Would a salinity of 30ppt adequately explain the STN? Alk has been stable within 0.7 dkh, more recently consumption has slowed down a bit to 0.3dkh per day. Testing and dosing once per day at the same time is keeping alk dead on at 11.5 dKH when I test every morning. This number is high, but nutrients in the system are high, and I dont want to bring it down until everything else is stable where I want it.

Assuming that salinity is the issue, should correcting this problem stop the STN, or will I most likely need to cut frags?

 

[jda]

It certainly won't help, but I have not seen too many issues until the SG is at 1.020, or so. I would get it back up to 35 PPT and also keep looking for other things.

I am not a dude who freaks out about alk like so many others, but 11.5 is pretty high. More around 7 or 8 would be better. Neither the salinity or alk would do this alone, but perhaps a combo of both has be no bueno.

 

[dtruitt]

It certainly won't help, but I have not seen too many issues until the SG is at 1.020, or so. I would get it back up to 35 PPT and also keep looking for other things.

I am not a dude who freaks out about alk like so many others, but 11.5 is pretty high. More around 7 or 8 would be better. Neither the salinity or alk would do this alone, but perhaps a combo of both has be no bueno.

Truth be told, I dont know exactly where to put salinity. The scales on the red sea refractometer dont line up with the theoretical conversion rate. Calibrated for SG, I'm seeing a reading of 1.020, calibrated for ppt I see a reading of 30 or theoretically 1.022sg... Getting the LFS to check the salinity today so I have another data point.

Alk spiked due to carbonate in well water making it through a "good" DI resin. It seems I get about 30 gallons before I need to replenish the resin. I've held alk steady at 11.5 figuring high stable alk is preferable to another 1.5dKH+ change, at least until everything else is sorted.

Nutrients are high enough to support the elevated alk, and as I understood it, high alk tends to burn tips. I did actually lose a PC rainbow to STN before the alk spike event, leading me to believe that parameter may not be a consideration.

I recently ran a poly filter and run GFO and Carbon 24/7, so I'm doubtful that metals are an issue currently.

 

[Beardo]

GFO can cause some issues if you are stripping phosphates too quickly.

On the Red Sea refractomer... I found them to be garbage. I had one and could calibrate and 10 minutes later it was off again. I ended up purchasing a VeeGee and chucking the red sea in the garbage. The VeeGee has been great; holds cal and is easy to read.

 

[dtruitt]

GFO can cause some issues if you are stripping phosphates too quickly.

On the Red Sea refractomer... I found them to be garbage. I had one and could calibrate and 10 minutes later it was off again. I ended up purchasing a VeeGee and chucking the red sea in the garbage. The VeeGee has been great; holds cal and is easy to read.

I suppose that some of this STN would coincide well enough with me tossing a new bag of GFO in the sump last weekend. This would also coincide with the last water change with water that was likely (but not 100% definitely) shy of 35ppt.

Should I really be concerned about stripping phosphates too fast with a passive bag of GFO in the skimmer compartment, though? I understood this to be a serious concern with reactors, but it's always taken me weeks to strip enough phosphate to see a change on a salifert test.

I'm going to get a conductivity probe. The more I read about using refractometers to test salinity, the less I trust them. There are too many places for device and human error to skew readings.

 

[dtruitt]

GFO can cause some issues if you are stripping phosphates too quickly.

On the Red Sea refractomer... I found them to be garbage. I had one and could calibrate and 10 minutes later it was off again. I ended up purchasing a VeeGee and chucking the red sea in the garbage. The VeeGee has been great; holds cal and is easy to read.

I just tested phosphates again, no measurable change since I added fresh GFO.

 

[Beardo]

I just tested phosphates again, no measurable change since I added fresh GFO.

What are your phosphate levels?

Also, I assumed you were running gfo in a reactor, I should have asked.

 

[dtruitt]

What are your phosphate levels?

Also, I assumed you were running gfo in a reactor, I should have asked.

Phosphate stays high at 0.5ppm. In this tank, P at 0.50 hasnt caused any notable algae issues or inhibited calcification as far as I can tell.

I feed a TON of reef frenzy and broadcast feed reef rods twice a week. Somehow, I only have to use the magfloat twice a week to keep up with the film algae on the glass.

 

[dtruitt]

Just got back from the LFS. Owner checked my sample with his refractometer and read 1.025sg.

I got back home, recalibrated my red sea unit again, and measured 30ppt again.

I'm at a bit of an impasse. I generally trust that the LFS owner knows what hes doing much better than I do, his advice has very rarely steered me wrong. OTOH, I've recalibrated and re tested so many times so many different ways that I'm inclined to trust that our tanks water is about 5ppt lower than it ought to be. I believe I will continue raising the salinity, along with other good husbandry and generally effective remedies for SPS issues: increasing flow, conducting more water changes, and periodically turkey basting problem corals.

Assuming that low salinity was a stressor, should I begin cutting frags, or should I wait for salinity to rise to see if the recession stops when a known stressor is removed?

 

[thatmanMIKEson]

Just got back from the LFS. Owner checked my sample with his refractometer and read 1.025sg.

I got back home, recalibrated my red sea unit again, and measured 30ppt again.

I'm at a bit of an impasse. I generally trust that the LFS owner knows what hes doing much better than I do, his advice has very rarely steered me wrong. OTOH, I've recalibrated and re tested so many times so many different ways that I'm inclined to trust that our tanks water is about 5ppt lower than it ought to be. I believe I will continue raising the salinity, along with other good husbandry and generally effective remedies for SPS issues: increasing flow, conducting more water changes, and periodically turkey basting problem corals.

Assuming that low salinity was a stressor, should I begin cutting frags, or should I wait for salinity to rise to see if the recession stops when a known stressor is removed?

Hmmm

 

[thepotoo]

Should I really be concerned about stripping phosphates too fast with a passive bag of GFO in the skimmer compartment, though?

Never seen it myself, but I've definitely heard of people losing tanks from stripping PO4 too fast. You're not doing that though given the detectable PO4. What do the growth rates look like? Lots of good growth tips? If not, I would bet on the PO4 being too high. Especially if your colors are a bit dull.

What's your PAR, nitrates, calc and mg? Check for pests, it's always pests.

Just got back from the LFS. Owner checked my sample with his refractometer and read 1.025sg.

Your LFS keeps corals, right? And has been in business for more than 2 years? If so, I would trust the LFS for the moment and pick up a new refractometer and a calibration solution, and don't mess with salinity until they arrive.