Persistent SPS dying off - no known cause.

[Fisherman Joe]

Get Cipro or Oxylinic Acid and treat the tank for possible bacterial issue. It's safe and, if bacteria are to blame, very effective.

Thanks. I’ll hold off for now, but will have to consider it. Yes.

 

[Fisherman Joe]

Some slight corrosion in the MP40 shaft. Could this be the reason?

Wouldn’t this show up something on a recent ICP?

 

[dwest]

Some slight corrosion in the MP40 shaft. Could this be the reason?

Wouldn’t this show up something on a recent ICP?

No I don’t think so. I’ve been using mp40’s since they came out and see that periodically without a problem. If the mp40’s are a problem you’ll see splitting on the magnets themselves.

I don’t remember everything you’ve looked at but you mentioned the dino sand sweep. If you are using the sweep over just the sand bed, I don’t think it’s a problem. But if the corals themselves are getting hit with UV light directly, that certainly can be a problem. Barring that situation,I would be more concerned about the dinos themselves. Some are very toxic to corals.

 

[sjfishguy]

What are you checking your salinity with? Get a tropic Marín hydrometer and make sure the salinity is what you think it is. All the other tests don’t matter if your salinity if off

 

[dwest]

Yes, looking back at your thread, I would correct and stabilize salinity if you haven’t done that already.

 

[Fisherman Joe]

My salinity has been a little up and down. I measure with a D&D refractomter and the GHL conductivity probe (but this is old now, still calibrated however) - I’ve had no more swings with salinity than I have during the last 5 years of my tank - but I am on NYOS salt now, not Tropic Marin pro reef salt (I switched in Nov 2025) - I Am guessing but maybe the Nyos salt is a bit more unforgiving?

Regarding the UV I am only hitting the sand and the dinos. Maybe them dying could be releasing something into the water? I dunno.

 

[Fisherman Joe]

I don’t think the wetside is rust, it looks like GFO staining the ceramic shaft.

 

[dwest]

My salinity has been a little up and down. I measure with a D&D refractomter and the GHL conductivity probe (but this is old now, still calibrated however) - I’ve had no more swings with salinity than I have during the last 5 years of my tank - but I am on NYOS salt now, not Tropic Marin pro reef salt (I switched in Nov 2025) - I Am guessing but maybe the Nyos salt is a bit more unforgiving?

Regarding the UV I am only hitting the sand and the dinos. Maybe them dying could be releasing something into the water? I dunno.

But some earlier posts suggest that your salinity is closer to 40 ppt rather than our typical target of 35 ppt. I didn’t see where that was addressed.

Anyway, good luck to you.

 

[mfollen]

Hello
Sorry for your losses and troubles… it’s tough for anyone to go through those stretches

I agree salinity can be very hard to measure and could be a culprit. Maybe its worth doing a separate company ICP (such as oceamo) and have a third party evaluate the salinity measurement (and other heavy metals) to get a another perspective and verified measurement.

Best of luck moving forward

 

[Reginald Reefer III]

One other potential option is witchhazel treatment.

Witchhazel Reeftank Treatment

Witchhazel Reeftank Treatment RTN/STN Resolution via the Witchhazel Tank Treatment The famous Witchhazel Treatment to support RTN & STN tank issues originated from Andre, completely rewritten and updated and now available outside of Facebook ;-)As many know the success to resolve this terrible...

reefmoonshiners.com

 

[hatfielj]

What are you checking your salinity with? Get a tropic Marín hydrometer and make sure the salinity is what you think it is. All the other tests don’t matter if your salinity if off

I second this BIG TIME. When I first set up my current tank, I was using an older refractometer that I had calibrated several times with brand new solution from my LFS. I was still suspicious that my salinity was off though, so I decided to check with a cheap hydrometer and found my number was way different than the refractometer. SO, I finally decided to order a Tropic Marin High Precision floating hydrometer and I am SUPER glad I did, because my salinity was WAY off (like 1.020!) Now, the tropic marin hydrometer is the only tool I use for checking salinity. It's the only one that doesn't need calibrating and is always correct. I just have to make sure to correct for temperature, but otherwise it's 100% reliable.

 

[slingfox]

Being very direct and frank:
Stop running around in blind panic and naming random parameters. Start acting on all the advice given here.

If you are looking for an “add this product and tomorrow everything will be fine” answer. You’re not going to get that.

The parameters in that ICP don’t look okay. As mentioned by several on this thread, you should doublecheck how you are measuring salinity. From the ICP, it looks like salinity is too high. If you can eliminate erroneous salinity measurement as an issue then you can focus on other issues.

There are many threads on this forum about measuring salinity correctly. The most highly recommended instrument is the TM Hydrometer. If you go the refactored route the only one that i have found reliable is the VeeGee. You may also want to use an ICP test which measures your salinity since this looks like a potential issue in your tank.

 

[slingfox]

Some slight corrosion in the MP40 shaft. Could this be the reason?

Wouldn’t this show up something on a recent ICP?

This is not related to the issue at hand: Do you grease your MP40 with Molycote when you clean it periodically? I don’t see any silicon grease but maybe it has already been wiped off.

Regarding the picture: That doesn’t look good. How often do you disassemble and clean your MP40s? If this didn’t show up on the ICP I doubt it caused the tank crash.

 

[Randy Holmes-Farley]

I second this BIG TIME. When I first set up my current tank, I was using an older refractometer that I had calibrated several times with brand new solution from my LFS. I was still suspicious that my salinity was off though, so I decided to check with a cheap hydrometer and found my number was way different than the refractometer. SO, I finally decided to order a Tropic Marin High Precision floating hydrometer and I am SUPER glad I did, because my salinity was WAY off (like 1.020!) Now, the tropic marin hydrometer is the only tool I use for checking salinity. It's the only one that doesn't need calibrating and is always correct. I just have to make sure to correct for temperature, but otherwise it's 100% reliable.

I hope your copy of that hydrometer was accurate. I always recommend testing any device with a proper standard. The fact that is cannot be adjusted does not necessarily mean is was properly manufactured, or remains properly calibrated after manufacture.

 

[hatfielj]

I hope your copy of that hydrometer was accurate. I always recommend testing any device with a proper standard. The fact that is cannot be adjusted does not necessarily mean is was properly manufactured, or remains properly calibrated after manufacture.

How would one go about checking the accuracy of a hydrometer? I would need at least 500 ml of a standard for it to float.

 

[slingfox]

How would one go about checking the accuracy of a hydrometer? I would need at least 500 ml of a standard for it to float.

Reef Aquarium Salinity: DIY Calibration Standards

Reef Aquarium Salinity: DIY Calibration Standards By Randy Holmes-Farley One of the most important issues facing marine aquarists is providing a suitable environment for their aquaria's inhabitants. Among the important properties for a marine...

www.reef2reef.com

 

[Fisherman Joe]

I hope your copy of that hydrometer was accurate. I always recommend testing any device with a proper standard. The fact that is cannot be adjusted does not necessarily mean is was properly manufactured, or remains properly calibrated after manufacture.

I bought some calibration solution for my Refractometer.

I studied biomedical science at university, so I recall calibrating every piece of equipment before using it!

Personally I think refractometers are easiest to use, as you can calibrate them very quickly.

My salinity hasn’t been super stable, my skimmer was skimming really wet for a long time. I’m hoping this is just a prolonged reaction.

My alkalinity was up at 9.5 too. I have lowered my dosing of triton reagents to 25% of what they were some months back with a fully loaded tank and it’s still not dropping past 9.0 yet.

I’m trying to do everything slowly now! I am noticing some explosive coralline growth on the glass the last week which is good!

I wanted to keep this thread super detailed for others to follow in future, so they can check one by one if they have these issues.

Oh and I checked for leaky voltage with a multimeter. It isn’t that.

 

[slingfox]

I bought some calibration solution for my Refractometer.

The above is the flaw in your approach. Commercial calibration solution cannot be trusted. I purchased calibration solution from three different providers and that is how I found out they are not reliable. This topic has come up multiple times on this board and there are numerous examples of people using cheap refractometers with off the shelf calibration solution and then finding out their salinity was way off.

You can make your own calibration solution using the instructions provided above for pennies.

 

[hatfielj]

Reef Aquarium Salinity: DIY Calibration Standards

Reef Aquarium Salinity: DIY Calibration Standards By Randy Holmes-Farley One of the most important issues facing marine aquarists is providing a suitable environment for their aquaria's inhabitants. Among the important properties for a marine...

www.reef2reef.com

Thanks! I’m going to try to make my own next chance I get.

 

[sjfishguy]

Refractometers have way too many variables that can go wrong. ICP confirmed my hydrometer was spot on at 1.0265 exactly