Flesh on all euphyllia receding

[asome_one]

As the title says, I have long struggled to maintain flesh on the stems of my euphyllia. The heads are generally pretty good. I don't typically see the corals losing tentacles or heads. At night they don't recede into the body more than is normal. I have 2 tanks, side by side, that run relatively similarly—same water change schedule, similar water chemistry, similar equipment, lightning, feeding etc. This has been something I have hoped to see improve over the year that I've kept all these corals but things have more or less stagnated.
I feed LRS with some reef roids twice a week, have a pellet dispenser that runs once a day, and occasionally give some red sea energy AB+
Both tanks are on dosing pumps with AFR and I switched to B-Ionic salt about 8 months ago, used reef crystals prior.
Left tank is dosed with vinegar due to a high bioload and a problem with nitrates (kept in check for 6 months)
I shoot for a mag of about about 1450 my water changes are typically around 1450-1500 mag.
I noticed my mag has recently been going a bit lower. 1350-1400 instead of 1500. however, drops of 100 mag in a month is not likely and i attribute it more to an issue with my test kit as that is the very high end of the seachem kit. Water changes going in read 1500.
Light schedules run for about 9 hours a day.

I have noticed that other LPS in both tanks grow but dont do spectacularly. Favia, acans, leptos exsist and look good in general. Soft coral is about the same with some zoa and some not. Mushrooms and leathers growing normally.

Throughout the time I have lost one hammer that tried to reproduce but failed and it all died. I have also lost an avleapora and goniopora which I attributed mostly to being unable to cater to their low flow needs in such a busy reef.

I have flow positioned in such a way to prevent stingers from my torch from touching my hammers. However I'm awake alot of the night due to work and never notice stingers coming out anyway.

All this to say I am just concerned that the flesh on the base of all the euphllyia across both tanks slowly recedes. I observe my tanks quite often and I dont notice flatworms. I treated once for flatworms on the off chance but nothing came from it. I know its not normal for the flesh not to cover the entire structure. On my torches it covers more...but still less than when they were originally added. I took photos of just as the lights came on. I'll get more when the lights go off tonight.

Edit: I also have tested PAR and generally keep the euphillias in the left tank around 110-130. Right tank is 210 for the top and 110 for the middle

Left tank tests :
Nitrate 1
Phosphate.02
Alk 8.0
Calcium 420
Magnesium 1400

Right tank :
nitrate 1
Phosphate .02
Alk 8.0
Calcium 410
Mag 1400

 

[asome_one]

Night time photos

 

[Mr. Mojo Rising]

The only thing I really see is very low nitrate and phosphate.

 

[twentyleagues]

As euphyllia grow there will be more skeleton showing below the flesh band. Most of the pics look fine one was hard to tell. I agree that your nitrate and phosphate could/should be higher. If you are actively feeding the euphyllia those lower nitrate and phosphate numbers may be fine. I dont have a good metric as to how much flesh band there should be but I would say 1/2-3/4" below the tentacles is adequate. The way euphyllia grow is to split heads and add more skeleton under the polyp as it adds more skeleton the polyp will grow upwards and more skeleton will be exposed below the flesh band. The upward growth is typically slow especially compared to the splitting of heads if you notice quick shrinkage of the flesh band it may be nutrient deficient. If this is the case find something that they will readily consume and feed them 1-2 times a week.

 

[Gumbies R Us]

I would raise your nitrates and phosphates

 

[asome_one]

It's been such a balancing act with these nanos to either have nutrients shooting way up high above 30-50 and phos .3-.8 it's either way too high or low low. I'll up my frozen feed to 3 times a week and do a weekly ab+ dose.
Thanks guys! I appreciate it.