Help - Polyps Receding

[reefer1]

I need some help from the experts.
My 105-gallon tank is about two years old. I have a mixed reef (acropora, monitipora, favia, and chalices). In the last couple of weeks, some of the polyps have receded.
Both oregon torts (about 1.5" fully encrusted frags) polyps have receded.
strawberry shortcake (1" and encrusted on frag) polyps have shrunk
rhasberry limeade (1" and encrusted over plug) polyps have shrunk
2.5" red planet still has its polyps extended and encrusting over rock
4" JF blue-tipped extended
starburst and superman montipora growing crazy
all the favias look good except one - lemon lime favite has some white lines along a few ridges
all the chalices look fine

Water parameters: 1.026, 78 deg, 8.0 alk, 400 calc, 1340-1350 Mag, 1-2 ppm nitrates, 0 ppm phosphates (measured with Hanna or Salifert kits). Controller and dosing unit keeps parameters stable.

Last week, I cleaned the overflow, sump, return pump, and skimmer of all detritous
Yesterday, I replaced the rowaphos in reactor (thinking there may be phosphates)
No other changes in lights or flow

Any Ideas?
Thanks!

 

[rsav]

Red bugs? AEFW (acro eating flatworms)? Both are known to cause polyps to retract. I have had both in the past.

 

[reefer1]

I don't think it's red bugs or AEFW since I have not added anything new to my tank in a couple of months

 

[twilliard]

What are you feeding the tank?

 

[reefer1]

I feed phytofeast (15 drops), oysterfeast (15 drops), reef roids (one spoonful), and aquavitro fuel (8-10ml) alternating a different one each day. And I dose KZ amino acids 5 drops daily. I also add Seachem Nitrogen every now and then to keep nitrates above 1ppm

 

[hinovak]

Did this happen directly after you cleaned everything, or was this a problem before?

 

[reefer1]

The polyp started to recede before I cleaned everything.
Cleaning was one step trying to get everything back to normal

 

[hinovak]

Are you running any carbon for coral warfare? I doubt this may be the problem, but if things are growing fast, and you have a mixed reef, you never know.

 

[reefer1]

Yes, I have a bag of carbon hanging in my overflow right behind the inlet teeth so that the incoming water cascades over it. It is only about 2-3 weeks old. I change this every month

 

[hinovak]

Grab a flash light and look late at night to see if you have any hidden pests you were not aware of. Once again probably not what is wrong, but worth looking into.

 

[reefer1]

The only creatures I could see scurrying around were bristle worms. I am thinking about slowly increase alkalinity to 8.5 and calcium to 410-420 over the next week to see if that makes a difference. Any thoughts?
Any other suggestions?
Thanks!

 

[hinovak]

I personally keep alk higher than 8. Things got happy, and my alk dropped a little low at night and made my acros unhappy. I'm sure there are plenty of people that keep alk at 8 and do just fine. However I like some wiggle room, because I feed my fish allot, so I keep mine at 9.6. Try going up slowly a bit over time and see how they react. If nothing changes, at least you can eliminate that as a possible cause.

 

[reefer1]

I started out trying to target natural sea water. It's at 7dKH. This didn't work out too well so I adjusted to 8dKH over time. I've asked local reefers where their tanks are and most are higher. I like the idea of having some wiggle room.
Thanks for the advice!

 

[reefer1]

My alkalinity is up to about 8.4 now. Still no improvement. In fact, the "bleaching" of the lemon lime favites is slowly progressing and the sps polyps appear to have receded more.
I do remember that I added about 10lbs of caribsea live sand about a month ago. Could this be behind the polyps receding? If so, what should I do to combat the problem? Thanks!

 

[Wolff92]

As a precaution, because there is always a chance there are pests especially on SPS colonies such as gorilla crabs etc, I usually take a flash light and look at the colonies about an hour or two after lights out.

AEFW: you'll easily be able to see bite marks on the skin at night with a flash light. You will also be able to see red bugs easily.

As far as crabs they generally come out at night to feed and will also easily be spotted.

STN and RTN usually caused by alk swings but to be on the cautious side I say check at night.

Best of luck!

 

[Wolff92]

Also using gfo or rowaphos all of a sudden can cause STN because it has the tendency to strip the water quickly. That sudden change can adversely affect sps corals as well. I recommended using the suggested amount and only running It for a few hours a day over the course of a month while increasing the time by one hour each time until it's running 24/7. But if you have zero phosphates no need to run any of that.

 

[reefer1]

Thanks for the feedback. Alkalinity is pretty stable. I usually target feed my corals a few hours after the lights are out. I use a narrow flashlight to help aim the food. I have to say that I have never seen anything crawling around except bristleworms. How fast do these other pests move?
There are no signs or STN or RTN on the sps. I have one large lemon-lime favite (2" in diameter) showing slow signs of bleaching - over a 5-6 week period - along its ridges. (okay, maybe that is RTN.) I think it's just lacking nutrients.
Hear is some more information - Today, I did notice that my TDS meter reads 200 when first turned on and then settles to 004 after 5 minutes. I normally just start collecting water right away but read in another thread that it's a good idea to let the system run for 5 minutes first so I checked. My membrane is only 5 months old and I flush it all the time. Could this be part of the problem?
And what about the new live sand?

 

[reefer1]

Just realized that when I upgraded my RO/DI unit, the TDS meter is now after the carbon block and filter but before the DI cartridges. So, the TDS should be zero out of the system after the first 5 minutes.