Montipora Digitata

dR3ws3r · Jun 29, 2026

Hi,

I haven't had much luck with SPS corals so far, and my LPS luck is just so-so. After a long battle with SCA Dinos, my tank is looking better. My nutrients are higher, (nitrate = 9 ppm, and Phosphate = 0.2 according to my ICP test results I just received) as I have been trying to avoid another bout of Dinos, which might be a low nutrient issue (opinions vary).

So most of the corals in my tank seem to be doing better, and the Dino's treatment of Diatoms (through use of silicates), has mostly killed all the algae in my tank. And my silicates are actually now on the low side. So a few months ago I bought a dozen frags of various types. Two were Monitpora Digitata. I put them in a QT tank for about a month, then dipped and moved them into my main aquarium. I left them on a tray near the bottom for a week then put them into their final positions. After idk 2-3 weeks they looked like this:

And just yesterday I looked at them, and they now have just turned to this:

So being naive and totally open to suggestions, are they just bleaching out? Is there a guess at the cause? Any chance I can save them?

My Alk is about 8.2, and has been pretty stable. Calcium (according to ICP) is a little low, around 390. Mag is fine. They are pretty close to a powerhead and perhaps are getting somewhat direct flow from a powerhead, but one more so than the other, yet they are both showing the same issue.

I do have a PAR meter and it is roughly 120 ish at peak lighting where they are positioned in the tank.

Any thoughts or suggestions?

TX_REEF · Jun 29, 2026

the good news is it looks like the polyps are just retracted, rather than bleaching. Do you have nitrate and phosphate readings? Since you said Alk, is stable, and fluctuations there tend to be the culprit in similar instances I've experienced, the other culprit ive experienced is sudden changes in nitrate or phosphate.

dR3ws3r · Jun 29, 2026

TX_REEF said:
the good news is it looks like the polyps are just retracted, rather than bleaching. Do you have nitrate and phosphate readings? Since you said Alk, is stable, and fluctuations there tend to be the culprit in similar instances I've experienced, the other culprit ive experienced is sudden changes in nitrate or phosphate.

So Nitrate is 8, and phosphate is 0.21.
Right now I only dose Tropic Marin part B for alkalinity. I don't have "large" enough corals to really be taking it down by much, but as my calcium is slightly low, I was thinking about starting Part A as well or even thinking about Kalk.

I've been trying to get out of the mindset of dosing things, to get the tank settled. I do add about 3-5 ml of Phyto each night, but that isn't anything in a 155 gallon tank. And I've been doing that for over a year. So, it isn't a sudden change.

You think there is a nutrient change? I will try to test every 2nd or 3rd day and see if I can find a trend. I haven't added anything that would "directly" change them, like GFO or anything like that. I could run some activated carbon for a few days. I don't run it continuously.

One thing I have noticed is that the sand is "browning" a little bit. I haven't looked to see what it might be because I don't want to openly sob if it indeed Dino's again. But it is time to bite the bullet.

TX_REEF · Jun 29, 2026

As a last check, how about your RO/DI? that's the last thing that I occasionally run into - my corals will "tell" me that it's time to replace RO/DI filter elements / your RO/DI is possibly no longer 0 TDS.

But yes, I'd recommend somewhat regular testing on N and P because changes on those can cause coral unhappiness, along with Alk.

dR3ws3r · Jun 29, 2026

TX_REEF said:
As a last check, how about your RO/DI? that's the last thing that I occasionally run into - my corals will "tell" me that it's time to replace RO/DI filter elements / your RO/DI is possibly no longer 0 TDS.

But yes, I'd recommend somewhat regular testing on N and P because changes on those can cause coral unhappiness, along with Alk.

I have a trident, so I can see my alk ... and it never really has big swings. It has daily swings but they are relatively small.

I could see my nutrients creeping up over time, but as I said, I haven't been dosing anything to make them change dramatically. My Nitrates always fall into the 5-10 range. Phosphates can swing up and down, but usually it is a slow trend. I do keep a journal with readings but when I was dosing silicates, it really seemed like the silicates were affecting the reading. So I had a period where I didn't pay as much attention. And everything "looked" better than normal, so the sudden change seemed surprising.

I do the total ICP, and they test the RO/DI, and everything was zero. I will use a TDS meter and see if I get a measurement. I have never seen anything greater that 2 ... and that was a while ago. But I will look.

I appreciate your input. I kind of feel like I am inadvertently arguing against you, but I'm not. I keep a decent look at things in general, and wouldn't have thought nutrients, especially with my ICP test confirming things, but I guess something changed, or something finally "gave" for this to happen.

Can Monti Digi's get too much flow? Would the recessed polyps show on the high flow side if that were the case?

TX_REEF · Jun 29, 2026

I would want my RODI TDS to be a solid zero, for what it's worth. I see unhappiness arise anytime it goes over 1.

Yes, digis can have too much flow causing polyp withdrawal, but if you haven't changed the flow, I doubt that would be the cause.

You have to think about ANYTHING that might have changed recently, big or small, and one of the items on that list is likely the cause. It doesn't have to big a "big" change, just a sudden departure from the stability the coral was accustomed to.

Mr. Mojo Rising · Jun 29, 2026

IT sounds like you've got it in front of a powerhead, that could be a problem IMO, a back and forth sway is the best for corals. The lighting is also low for sps, even for lps actually, very few corals will thrive at 120 par IMO. If you really want to get into sps I would suggest to increase the intensity of the light.

X-37B · Jun 29, 2026

Its most likely just acclimating to your system.
Something may have been picking at it at night. Hermits or other crabs.
I get that look when I frag mine. It can stay like that for a few weeks when I frag it and move it to another system.
Constant direct flow from a powerhead can give that look also.
I run powerheads on Sea Sweeps so the flow is high but it sweeps across the coral and is not constant.
I fragged it from the 150 and put pieces in 2 different systems.
The 150 is 400 par, the 50 is 250 par, and the 112 is 550 par so they can take as much light as you can give them.
They will pale out in low light levels over time.

dR3ws3r · Jun 29, 2026

As you can see from the side view, the bigger monti is in front of Zip the yellow tang, and the smaller one is just to the left of the lower light reflection. Neither powerhead is "directly" on it, but pretty close. They run at 65% during the day and 20% at night. with a Nutrient transport and Reef Crest programs respectively. So, if I were to play detective, I would say it is strange that they "both" showed distress, when they are being influenced by different powerheads. Maybe? As they both showed issues, that sure seems to imply a common problem. Even if it was lighting, it would be pretty "odd" that after a month+ on the same day they had an issue.

KrisReef · Jun 29, 2026

dR3ws3r said:
As you can see from the side view, the bigger monti is in front of Zip the yellow tang, and the smaller one is just to the left of the lower light reflection. Neither powerhead is "directly" on it, but pretty close. They run at 65% during the day and 20% at night. with a Nutrient transport and Reef Crest programs respectively. So, if I were to play detective, I would say it is strange that they "both" showed distress, when they are being influenced by different powerheads. Maybe? As they both showed issues, that sure seems to imply a common problem. Even if it was lighting, it would be pretty "odd" that after a month+ on the same day they had an issue.

Light is the energy that keeps them growing. THey have been trying to grow, but at low light they are struggling and over time they are pooping out? More light energy. A longer daylight period, perhaps, to see how they respond?