Recent GHA explosion, why?

[ThRoewer]

Within the last few weeks I noticed a rather sudden and significant increase of green hairy algae in my 200 gallon system. What was a month ago just some ugly fuzz has exploded to thick plumes of green hairy algae. :headwalls:
The cyanos I had before seem to get less.

Because the nitrates and phosphates were rather high I started dosing vodka at the beginning of July. I'm currently at about 17 ml.

About two months ago I added finer gravel to have less detritus accumulating between the coarser gravel pieces.

Additionally I also installed a GFO reactor to drive the phosphates down.

I also added a MP 60 Jebao in wave mode to agitate the water of the 100 gallon tank into a wave motion.
Further I added a filter pump with filter floss (cleaned or exchanged every few days) to remove as much detritus as possible.

I added also 4 Tigertail Cucumbers (2 to the 100 gal, 1 to the 40B and 1 to the refugium) to deal with the detritus that might still accumulate.

The ground is now much cleaner and the cyanos that were there before are gone.

Last weekend I discovered that out RO system's membrane had gone bad and that the water I used for roughly the last 2 months was likely just mechanically filtered and dechlorinated tap water with TDS values round 250 ppm.

The tanks that are most affected are the 100 gallon and the 40B tank. Of course those are the ones with SPS.
The only tanks in this system without serious GHA are the 40B sump, likely due to the 2 large longspine urchins that constantly mill over the rocks, and the refugium, which has nearly no flow.

These are the recent water parameters of this system:

......................NO3.............PO4..............Alk............Ca...............Mg
17.05.2016 --- 25.0 ppm --- 3.00 ppm ----------------- 410 ppm --- 1230 ppm
13.08.2016 --- 25.0 ppm --- 0.36 ppm --- 7.0 dKH --- 375 ppm --- 1280 ppm
24.08.2016 --- 25.0 ppm --- 0.11 ppm
26.09.2016 ----- 5.0 ppm --- 0.30 ppm
04.10.2016 ----- 2.5 ppm --- 0.02 ppm --- 9.4 dKH --- 820 ppm* -- 6000 ppm*

Used tests: NO3: Salifert --- PO4: Hanna Phosphorus ULR --- Alk, Ca, Mg: Red Sea
(* seem to be seriously off - gonna have that checked at LFS later)

My 42gallon system got the same "tap water" refills and has NO3 and PO4 levels that are totally over the test's upper limits - I just stopped measuring it.
Yet in this tank 2 hermits and maybe 5 Trochus snails manage to keep the algae in check, the coralline is growing like crazy and the 3 SPS I have in there have a quite good polyp extension. So I don't know if the "tap water" can really be blamed (gets fixed anyway).

So I'm wondering what got the GHA to take off despite the nutrient levels going down?

Could the GFO add iron that fuels the GHA growth?
Do the GHA prefer lower nutrient levels?
What else could bring this on so suddenly?

Most importantly, how to fix it?

[Mark9]

Turbo snails.

[ThRoewer]

I already have some and they show no interest into the GHA patches. Also, they can't reach into tight crevices.

[Buzz1329]

"Last weekend I discovered that out RO system's membrane had gone bad and that the water I used for roughly the last 2 months was likely just mechanically filtered and dechlorinated tap water with TDS values round 250 ppm."

That may be the cause of the GHA. Unfortunately, changing RO membrane may not be enough to eliminate GHA immediately. But maybe other changes you made will help.

Mike

[ThRoewer]

I did some mechanical removal, though many places are not accessible.

I already have a bunch of snails and hermits in quarantine which hopefully can go to work soon.
And more hermits and snails are on the way...

[FullBoreReefer]

You already have urchins that will eat it, move them to the DT and let them go to work.

[Timfish]

Corals and algae are literally conducting very sophisticated biological and chemical warfare in their competition for the available nitrogen and phosphate. If you are stripping out your inorganic phosphate (PO4) and nitrate and not feeding your fish heavily on a daily basis to provide ammonia and urea and phosphate your corals will have problems with their zooxanthellea making sulfer compounds which gives any nuisance algae in your system the upper hand.

[ThRoewer]

You already have urchins that will eat it, move them to the DT and let them go to work.
I tried the large ones I have in the sump and they did more damage than good: they preferred to mill off the coralline algae over tackling the GHA and also just "machined" over corals that were in their way.
I have 4 babies in quarantine that may work better until they get too big.

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