Lethargic firefish and royal gramma, but clowns corals and crabs are fine, help/why?

[Wyoguy]

Hello all!
I am new to Reef Central but have always thought the forums here were the most helpful, so I decided to join!

I need some help with my fish please! I have 2 purple firefish, 2 clowns, 1 Royal gramma, 1 searpent star, crabs and snails, mushrooms, Zoas, and a candy cane coral.

I came home today and my firefish and Royal gramma are laying on the sand under my rocks and won't come out, they look really unhappy. My clowns and corals and invertebrates are happy so I am extremely perplexed as to what's happening... My water parameters are as follows

55 gallon with no refugium, one protein skimmer and two power heads

PH-8.2
Nitrite-0
Nitrate-30
Ammonia-0
Calcium-485
Temperature-77.8

I know my nitrates are higher than most would like but I can't get them down, I have been doing 20% weekly water changes for over a month and they just hover at 20-30

Can anyone offer any advice I have nothing left to try other than my 40% water change I am in the process of