Corals Bleaching and I don't know why

[772reefer]

I am having some trouble this month with my tank. The majority of my corals are doing fine but some of my sps have some bleached spots on them and losing color/polyp extention. The corals with problems are a ORA birds of paradise and a ORA green stylo, a pink birdsnest. I have other birdsnests, montis, and 1 acro that all seem to be unaffected and doing fine. I tested my water and got the results below. Only thing off from normal was Nitrate. Both corals have been in the tank for about 6 months and were growing well with good color. My LFS recommended getting my PO4 and NO3 back up above 0 so i have doubled my feedings, removed my bag of mixed carbon and GFO, removed my filter pad, and I only run the skimmer every other day. The only filtration left if my cheato which gets trimmed during the middle of each month to about the size of a softball. I am still testing 0 for PO4 and NO3 and the problem corals show no signs of getting better. The cheato is growing faster so i think those levels are rising but getting consumed. My refugium is about 10g on a 75g tank Any advice? Nothing has changed in my normal retinue in the last 10 months.
1.26 salinity
480 Calcium
8.5 alk
0 P04
0 NO3 (Normally around 5)

 

[tmcca]

You check your lighting Par? One thing I would check. Yea over using gfo can cause low P04 which can cause issues.

 

[772reefer]

You check your lighting Par? One thing I would check. Yea over using gfo can cause low P04 which can cause issues.

Would Par change if I have not messed with my lights at all? I don't have a Par meter to check but I would think PAR should be fine since all over corals are fine. The lights are Mars Aquas. Could they put out less Par overtime due to use? I don't have any burnt out lights.
I have always tested PO4 at 0 which was no surprise since I was using GFO. I only add a little to my bag of carbon. Maybe 1/10 of the recommended amount. Been running like that for over a year. Maybe the quality of the GFO/Carbon was a bad batch and stressed those corals?

 

[tmcca]

Well I was just discussing this actually running GFO may do more harm than good. Corals need nutrients in order to survive Nitrates/Po4 and too little will cause them to die or not look great. I would stop using GFO and if you have chaeto stop using it and see what happens. That would be my first thing. I would try and get some par readings if things don't improve.

Believe it or not you need Nitrates/Po4

I actually tested this with two tanks and ran both a year.

One tank measured 0 Nitrates/Po4 0.1 or undetectable running gfo/chaeto for 1 year
other tank ran gfo/chaeto only for first 6 months
that tank measured 5-10 ppm Nitrates/Po4 0.2-0.5 had some algae issues at first with this tank but not so much after one year

Both had same corals started with soft than went with lps

First tank corals looked not great but not bad either
Second tank corals flourished and looked way better

Bottom line:
Nitrates anywhere between 2ppm-10ppm any higher find a way to lower it
Po4 0.2-0.5 anywhere higher than maybe run GFO to lower it to the desired level between this

My theory is first 6 months tanks will have excessive nutrients that tank can't adjust to reason why excessive algae blooms.. after 6 months tanks come more stable and probably can get away with GFO regularly anyway.

Too much skimming as well can cause issues. As long as you don't have algae outbreaks you may have not enough nutrients in water.

 

[772reefer]

Ok so the route I am on now where I have removed the GFO,removed filter pads, cut back on skimming to every other day, and doubled up on feeding to raise nitrates and phosphates should help. Maybe trim the cheato more than once a month too since it is now growing even faster ( softball size to almost filling 10g area in 2 weeks, usually takes a month). Didn't want to remove all the cheato as it is the other filtration I have on days the skimmer isn't running.

I was recommended by friend to try adding another fishing to raise nutrients. I currently have a yellow tang, flame angel, diamond goby, lyretail anthais, a small foxface, 1 cleaner shrimp 1 coral shrimp. Would another fish be too much for a 75g. Kinda seems like my filtration would handle it and it should help raise the nutrients.

As for Par readings might be a while before I can get that as I LFS doesn't have one or know anyone in the area I ca borrow from. Probably have to rent from BRS. Was thinking of getting new lights one of these days since there is more info on the web about Par at specific settings of lights like AIs or Radions than for Mars Aquas.

 

[JPergamo]

I'll 2nd the removal of GFO. For years I always stripped all nutrients always worried about algae and chasing 0s. Tank is dirty as hell now as far as NO3 and PO4 but a few years old. Minimal algae, corals thriving, fish fat and overfed.