Paly disappearing

[Rmckoy]

I have no idea if this could be lights or what the reason could be .

230 gal tank running for 3+ years. Transferred from my 90
That’s been running for over 10 years

The palys were added on the one rock and spread up to the rock on the right and completely covered everything .

The last 6 months they are slowly receding and not opening

Could t5’s lighting be the cause.
Parameters are stable and always
7.5 dkh
1.026 sg
425 cal
<5 nitrates
But phos fluctuates from 0.07 -0.2 at its highest and within several months

I suspect something picking on them or lights are not enough ( but having a hard time believing 8 bulb t5’s not being enough light

The palys are within the bottom 6” of the tank which is 27” deep plus 6” above the water is where the lights are

 

[blaxsun]

Mine have been disappearing over the past year. I know it's a nibbler - I've just never caught him in the act.