aquarium advice

[lonphi49]

Hello,
I'm very new to saltwater aquariums. I've had my aquariums for about 2 months now, and for a while, everything was going great, but then I started having some bad spikes in my ammonia and nitrate/nitrite lvls, although the tank was cycled via shrimp, and was left to run for a month.

I've lost only 1 fish so far (copper banded angel) and now my yellow tang, I believe is getting/has HLLE.
My question, is am I set up wrong, or doing something wrong??

My set-up:
75g - red sea salt mix, tap water dechlorinated (i know this isnt the best)
2x 60gal hanging power filters with the regular blue insert that has carbon inside
1x 450gpm powerhead
1x 150w heater
1x 50w heater
2x air stones c 60gallon air pump
40lbs live sand
two lg rocks i picked up in the forest and thoroughly cleaned
sea shells, and assorted lg pebbles
lighting: 5k watt actinic
5g quarintine c hanging power filter and air stone and halogen light

Fish:
1-Yellow tang, 1-blue damsel, 1-banded brittle starfish, 1-clownfish, 1-blue-spotted goby

Chem:
pH - around 8.4, 8.5,
alk - 300ppm
ammonia - .25-.5ppm
Nitrate- 20ppm
Nitite - 3.0ppm
Chlorine - 0
Temp - 79f
Salinity - 1.021

Food:
Nutrafin tropical fish pellets alternating c dried brine shrimp

Additives:
bioenzyme biological additive
tetra aquasafe for tap water
API stress zyme to try to get my nitrites under control
Tetra easy balance to try to get nitrates under control.

I've had a few instances where my fish looked very distressed, breathing very very fast, staying near the bottom and i did a massive water change immediately which seemed to help, but i dont understand what the problem is with a seaminly cycled tank, having these problems.
BTW the angel that died, i'm not convinced it was from water quality, i didnt notice at the FS, but he has a tumor-like growth on his nose and a very high blood supply viewable through the skin, and looked like he couldnt open his mouth all the way. unfortunately the store does not accept returns, so i couldnt take him back once i noticed it.

Please, any advice would be great!

[7digits]

You got the rocks from the forest? That could be a major problem there. You need live rock from the ocean. That rock that you have could have metals in it and that would cause all kinds of problems. Take them out now! Get some cured live rock. May I suggest that you read the sticky's on this site and start over from the beginning.

[ToddTT]

You need to read *all* of the stickies on this forum. Starting with this one for your Tang, ASAP:

Feeding Marine Fish and Fish Nutrition

Pick up some frozen herbivore blends, and some dried seaweed sheets with a $2 plastic clip on a suction cup... today!

Also look into supplements like Zoe and Zoecon, or others as mentioned in the above link.

A protein skimmer will greatly help with water quality.

Water changes as well, but you have to stop using untreated tap water. Ideally you would have purchased an API tap water filter instead of multiple fish.

Do not add any more livestock until you get your Tang back to health. This will serve two purposes... reducing stress in the tank, and ensuring that your tank is capable of providing a healthy environment.

Coming here was a good idea. Keep asking questions, and keep us updated.

And +1 on removing the rock from the forest. Do that before you leave to buy some non-pellet food!

[ToddTT]

ammonia - .25-.5ppm

You need to do a large water change ASAP. Your ammonia and nitrites are toxic to your fish.

Start dissolving some salt with a pump right away, and add that tap water filter to your shopping list for today.

More links to read:

How to Make a Successful Water Change

Setting Up a FOWLR Aquarium

What is Water Quality

It sounds like your biological filtration is not up to the task, or your tank is not fully cycled. Others will have more advice on this front.