Pavona Cactus bleaching

kblazewicz

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Hi!

I'm new to reefkeeping, I've bought a complete, mature all-in-one tank (Red Sea Max Nano) with plenty of corals inside. I'm aware that because of that, I've skipped all the lessons of starting the tank, coral selection and introduction, parameters tuning and so on. I'm doing my best to learn how to take care of a saltwater tank, but in this situation I feel kind of hopeless. Enough of the introduction lets get to the issue I'm having.

One of the coral species I bought with the tank was (correct me if I'm wrong) Pavona Cactus, total of 3 colonies, each 5-7 cm wide. Here you can see picture of one taken soon after the tank was moved and rescaped.

IMG_20201007_172806.jpg


I looked pretty healthy, it had nice deep color and looked fluffy with all the polyps extended.

Unfortunately few weeks later it looks terrible. Please excuse quality of the photo, its deep into the tank and I can't do any better than that.

IMG_20201026_194834.jpg


All 3 colonies lost most of its color, they barely extend any polyps, it looks like they're dying.

About the parameters now, I think the key might be in there.

Currently tests show following parameters:

Salinity: 35 ppt (handheld refractometer, calibrated with Salifert Refracto Check 35 ppt fluid)
Temperature: 27 deg C (without a heater, pumps must heat the water a lot)
Ca: 470 ppm (Salifert)
Mg: >1500 ppm (Salifert, its 1570 ppm if I go over the nominal scale)
Alk: 7.7 dKH (Salifert)
NO3: <0.5 ppm (Salifert)
PO4: 0 (Zoolek)

But when I first got the tank the alkalinity was only around 5 dKH. I have dosed sodium bicarbonate and some sodium carbonate to bring it up to 8.0. I tried to do it slowly, no more that 0.5 KH with each dose, the rise from around 5 to 8 took me 3 days. Since then I see a drop of around 0.3 dKH per day, I'm keeping it up with sodium bicarbonate solution. I plan to add Calcium Hydroxide (Kalkwasser) to my ATO to keep it stable. Other parameters looked Similar

Also previous owner did 20% monthly changes with NSW. I do 10% weekly with synthetic, I use Aquaforest Reef Salt.

All Pavona colonies are placed high in the tank, with plenty of light, water flow is not too strong in there.

Do you think I can do anything to save the corals at this point? Could they possibly recover?
 

C. Eymann

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Both nitrate and phosphate levels are a bit too low, Id shoot for 3-5ppm nitrate and .04-.08 phosphate.

anyway temps may have gotten above 27°C ? high temps , esp if exposed to intense lighting can result in bleaching, pavona seems to be more sensitive than other sps when it comes to temperature related bleaching IME.
 
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kblazewicz

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Both nitrate and phosphate levels are a bit too low, Id shoot for 3-5ppm nitrate and .04-.08 phosphate.

I have two clownfish and one six line wrasse. I feed once a day with frozen artemia, should I feed more to get NO3 and PO4 higher?

If its very important I could get some sodium nitrate and sodium phosphate.

anyway temps may have gotten above 27°C ? high temps , esp if exposed to intense lighting can result in bleaching, pavona seems to be more sensitive than other sps when it comes to temperature related bleaching IME.

I admit it was unstable during this first weeks, It did swing between 23 and 28 °C. I Installed a heater set to 25 °C so it doesn't get too cold when the window is open in the room.
 
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kblazewicz

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Both nitrate and phosphate levels are a bit too low, Id shoot for 3-5ppm nitrate and .04-.08 phosphate.

I believe that's the case!

I bought Milwaukee MW12 phosphate colorimeter (specs identical to Hanna HI713, I'd bet its exactly same hardware inside) and my water tested at 0.00 ppm PO4.

I started feeding 4x more than I did before and after a week still couldn't get my nutrients do detectable levels. Then I started dosing Na2HPO4 and KNO3.

Dosing potassium nitrate quickly bumped NO3 to around 1 ppm and it stays there with my intense feeding. One side effect I noticed was that my alkalinity got full dKH point up, from ~8 to >9. I didn't realize dosing NO3 causes alkalinity to rise.

With disodium phosphate I still have to find good dosing quantity, currently I add ~0.06 ppm PO4/day and yet it haven't got >0.00. Few times I tried bumping 0.05 ppm at a time, 10 minutes after the dose MW12 shown 0.06 ppm but 2 hours later it was back to 0.00. I'll try to get it to stable 0.04 ppm by slowly increasing doses.

It seems that my attempts to rise NO3 and PO4 did bring positive effects to my tank, all pavona colonies slowly start to regain their purple/brown color already :) Also some of my soft corals got better colors.

Whats interesting, even with undetectable NO3 and PO4 I have quite a lot of GHA and cyano on some rocks. Where did they get their nutrients from?
 
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kblazewicz

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I thought it was GHA, but after some research I'm starting to think its actually dino. This would make sense since dino thrive in tanks depleted of nutrients.

Cyano on the left and supposed dino in the center.

cyano_and_dino.jpg
 
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homer1475

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Looks more like cyano, and regular old GHA to me. Don't see the typical snotty, bubble looking algae. Just slimy mats indicative of cyano, and the long wavy GHA.
 

Do you have a frag tank, frag rack or some other place for coral frags currently?

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