Acropora RTN...

Rosie · Jan 25, 2020

Ok I'll start from the top...

I went to feed my fish this morning and I noticed my green staghorn acropora melting away! It was perfectly fine yesterday. One of the hermit crabs was sat in the branches eating the dead tissue.

So I've immediately tested my tank:

PH: 8.1
Salinity: 1.027
Alk: 7dkh
Mag: 1320ppm
Cal: 355ppm (I recently discovered my dosing line had calcified so I'm in the process of raising this)
Nitrate: 1ppm (fighting to raise this)
Phosphate: 0.015 (again I'm trying to raise this)

My tank is 5 years old
Lights: ATI Sunpower T5s
RTN Acropora age: 13 months in tank
The last coral I added was over 6 months ago

Dosing: I automatically dose Alk, Mag and Ca

I have just started automatically dosing Seachem flourish nitrogen to help raise my Nitrates, I'm starting very low and im getting a steady reading of 1ppm when I test Nitrates

I am currently hand dosing vibrant to tackle turf algae which has recently made a reappearance...

I am not running any chaeto, I took it offline a long time ago due to it being too efficient and stipping all the tank nutrients. I just have a skimmer to deal with waste export. I only run Carbon on the rare occasion that I think I need it.

What I did on the days and weeks running up to the RTN:

- Restarted Vibrant (2 weeks ago), I've never had this problem when dosing it previously

- Started dosing Seachem flourish nitrogen (yesterday... 24.01.20)

- Vacuumed my sump (yesterday), I hadn't cleaned it in a long time and it desperately needed it

- Made slight adjustments to my automatically dosers for Alk, Ca and Mg. Nothing major, just small increases to account for what the new growth is using up (this has taken me a couple of weeks to fine tune)

As I read this I'm starting to think I've done too much over a short space of time and this is possibly the reason for the RTN??

What I've done so far since discovering the RTN Acro:

- trimmed back the acropora to remove all the dead tissue and hopefully try to save what's left

- Added carbon

- I've not made any changes to anything I'm dosing as I didn't want to unintentionally upset the tank any further

I think that's everything I can think of? Any ideas of what could have possibly caused it or any tips on what to do next would be massively appreciated.

Reefer40b · Jan 25, 2020

It could have been just fighting with the stylo next to it, sometimes they can give up pretty easy. Hows your other corals look?

Journeyman · Jan 25, 2020

My guess is the vibrant. Probably it's stepping nutrients too fast.

Rosie · Jan 26, 2020

Thanks for your replies, it didn't have a good night last night. It lost the majority of it's colour in it's remaining tissue. I'll just leave it in there to see if it ever regains life again...

The corals around it look happy enough this morning.

And the tank in general is ticking by nicely, this was shortly after the full set of lights came on this morning.

happysalt · Jan 26, 2020

I agree with the vibrant causing this issue. Other corals in the tank seem like heartier species. unfortunately whenever my levels in my tank are within acceptable ranges but close to the limits of whats healthy and something changes, then thats when I always lose something. Try and get those nitrates and phosphates up a bit and that way in the future if a new stresser arises your corals will be healthy enough to deal.

My 2 cents.

LARedstickreefer · Jan 26, 2020

I don’t think those levels of nitrate and phosphate are too low. At least not to cause rtn. I’ve never seen low nutrients cause rtn, just a loss of color and growth over time.

I think that Vibrant, in some cases, is the direct cause of death. It supposedly kills algae on contact as well as dropping nutrients. I bet some corals are susceptible to direct contact with Vibrant.

TexasReefer82 · Jan 27, 2020

I've definitely had low nutrients be the cause of STN on Acropora and I know this because I was able to arrest the STN and achieve rapid recovery by dosing phosphates which were at zero.

Something else to consider: How are you measuring the nitrate and phosphate? If the phosphate was measured on a Hanna ULR checker then I would indeed believe the 0.015 value. However, if it was measured on any test kit that uses the human eye to compare the sample to a color chart I would not believe it - it's probably zero.

Also, what nitrate test kit are you using? My Salifert test kit will give me a reading of 1ppm - but when I sent the same water sample for an ATI ICP test (which uses Ion Chromatography to measure NO3) it comes back as 0.01 - effectively zero.

So... your nutrients may in reality be way too low. And Vibrant isn't helping that situation. I like Vibrant and I use it sometimes. But I suspect that after a certain period of time in use it also will affect our most sensitive corals (acropora). Perhaps it starts to attack the zooxanthellae itself??? I don't know, just speculating.

SeaDweller · Jan 27, 2020

I see metal hose clamps, are you using them anywhere else where they could rust, and be dripping into your tank or sump? I only see one acro colony in there (was), and the other stuff is more forgiving, IME.