Opinions Needed: Red Tabling Acro RTN



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May 24, 2020
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Hey everybody, need some opinions and thoughts on the possible cause of RTN for just one of my Acros.

Back story, a couple days ago my Red Tabling Acro went into RTN. It's the only acro that did this as I have many more in my tank that appear healthy, full polyp extension, forever expanding encrusting and growth, etc... Trying to sort out the cause. Nothing has changed in my tank for a few months in terms of routine, maintenance or additions of dosing, fish or coral.

The one thing that has changed is summer weather in the North East. With my windows open all day, I am able to change my pH from a low of 8.0 and a high of 8.15 to a low of 8.2 and a high of 8.35 during the day/night swings. As well, the temperature has increased which seems to have pushed my temperature a little high than normal (Normal average is 79F +/- 1F, now its 79.5F +/-1F).

Then, the other day (about 4 days prior to the RTN event) it got super hot (into the mid-90s), so I closed all my windows and threw on my AC which then dropped my pH from a day time high of 8.35 to 8.0 and then cycled a few days between 8.0 and 8.15 like it would normally do with the windows closed. This in turn caused a bit of an ALK spike (average running in the tank is about 7.5dKH, this moved it to 8.75dKH).

Then today, I noticed on the base of the Acro two some what small Aiptasia (which I found weird cause I haven't added coral to my tank in about 6 months and have seen no signs of Aiptasia anywhere else). So I pulled the whole frag, sucking some water out with it in case the Aiptasia decided to spew babies (fingers crossed here).

So now, as I am still determining a possible cause and knowing that I need to look back days or weeks at different events that occurred for RTN, I am looking for the communities opinion (assuming testable parameters* are within acceptable ranges);
1. Would this changes in pH and Alk from closing the windows be a possible cause?
2. Would a sustained spike in temperature over 80F be a possible cause (sustained = 6+hrs one day)?
3. Could the sting from these two small Aiptasia's start a RTN event?

I have an ICP test out the door to give me some more insight into the different parameters just in case something else is there but I don't have those results back yet.

Also, no chemical spraying in my yard or other outside activity to my knowledge other than a large amount of pollen from the trees coming into my house with having my windows open.

*Testable parameters:
Alk: 7.5
Cal: 400
Mag: 1350
NO3: 12
PO4: 0.03

In any event, this whole thing got me thinking about how to transition from open windows to closed windows in my house to help lessen the swing of pH throughout the day as coming from 8.35 to 8.0 in the matter of 10 hours seems a bit harsh when the normal swing is about .15.

Thoughts and discussion welcome, curious if I'm missing something else.
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Jan 28, 2018
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Of the issues you've outlined, Alk and the aptasia are possibilities but would surprise me. The temp and PH changes are very unlikely. Maybe the ICP test will reveal something but if it was a water quality issue I'd expect other corals to show signs.


Figuring out the hobby one coral at a time.
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Way upstate NY
I do the same living in the north east.

Temps fluctuations, and small ALK increases from opening the windows(higher PH, higher consumption)), to then closing them(lower PH, less consumption), and turning on the AC(my PH tanks with the AC on) has no effect on my reef.

Sometimes corals just die, unfortunately.

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