Long term tank issues

[Dr.Tankenstein]

Hello all, I'd really appreciate some help with this as I'm about to my wits end.

Tank specs: 40g breeder plumbed down to a 20g sump. 1 year old tank. Started with dry rock and cycled to for 2 months. Small sand bed. A gyre and chinese MP10 for flow on opposite sides. 2 older (5 years) kessil 360s that have been checked via par meter - 200ish at the bottom of the sand 300ish 6 inches under the water

Filtration: A ball of chaeto grown with an amazon LED that grows well. Filter sock changed 1x per week. Older (5 years) reef octopus skimmer and a carbon reactor. Return pump is a jebao - dont remember what kind but its enough to get the job done. Water is made from a 4 stage RODI unit that was recently checked via ICP test - came out with all zeros. Salt is just the usual IO.

Livestock: Green chromis, coral beauty angel, yellow coris and naokos wrasses. A few snails. A few hammers, blastos, and acans that I've had since the beginning of the tank.

Chemistry:
1.026 via recently calibrated refractometer, consistently there with ATO unit
temp between 78 - 79.5 via apex controller hooked to two heaters
Alk: Stable around 9.0 checked weekly
Ca: 440
Mg: 1400
Nitrate: Dosed to be 12 using pharmaceutical grade
PO4: 0.02-0.04



Rough tank history: After cycling the tank did quite well. Slowly added fish and the aforementioned coral. Had a decent sized acan garden going. Then for some reason about 5-6 months in acans started receding and dying of unknown cause. Seemed that it may have been bacterial as there was rapid spread from one colony and then to surrounding colonies. After this the tank bounced around a bit between good consistent growth and stagnation. A few months ago, got an ICP test that showed elevated tin and removed a powerhead that had rusted (also added a polyfilter at this point, since taken out), as well as changing how my filter socks are washed according to my LFS owner(orginally was spraying with water from hose and drying, moved to bleaching and then using dechlorinator + RO washes to remove). After this the tank did well for a month, probably better than it ever has. Growth took off and I was quite excited! Unfortunately in the last month this has stalled and in fact receded. I had two test SPS frags in the tank that went from thriving to basically dead in a matter of weeks.

Of note, there have been essentially no fish mortalities in the tank other than two that were within a few days of getting them shipped in. Fish are fat and happy. Just corals seem to hate the tank.

Would really appreciate any next steps from here as I'm out of ideas of what could be so drastically wrong with this tank. I've had saltwater tanks in the past and my brother did quite well with this exact setup but I think there is something systemically wrong with the tank that I am missing. The bad times have been far more numerous than the good.

Thanks for any advice, please let me know of any more info that would be helpful if it isnt posted here.

SC Reefer

 

[Troy V]

From what you've posted your system chemistry is in check. Assuming your test kits are accurate. If you haven't already I would recommend using different brand test kits to test for accuracy. I had a MAG test kit that was showing 800s when my MAG was over 1500.
I would put money that your problem is with your pharmaceutical grade PNO3 you are using to raise your Nitrate levels. I used this same method as well on and off for years, and eveytime I would use it I ran into a wall, where the overall system health would start to decline. It was frustrating because the SPS would color up beautifully just to decline a couple of months later. I no longer use the product and went with a more natural approach to raising my NO3 like feeding a lot more with auto feeders and going skimmerless.
This fixed my problems and the system is far healthier because of it. Good luck!

 

[Dr.Tankenstein]

I will update my kits, thats a good idea. Thanks! And interesting about the nitrate, I would never have guessed that!