Whitney,
Tap water isn't good. Most likely, some of your high nitrates are coming from the tap water. Humans can drink nitrates but your tank can't handle it.
I'd buy an RO unit right away. Thats going to be the first step in reducing your nitrates and assuring you are putting only the best quality water in your tank.
Scrape the algae off the glass right before you clean the tank. The thought process here is you will suck out some of it after you've scraped it off the glass. Not all of it, but some. Every little bit helps.
On a 55g tank, I'd be doing about 5g every week. That would be a regular maintenance schedule. But right now you are having water problems so I'd start out with 10g every 4 or 5 days until you get the water chemistry straightened out.
Reduce the bioload in the tank. Remove some fish. Reduce feeding for the remaining fish.
Are you feeding flake food or pellet food? What kind of fish? You need to be careful about what foods you introduce to the tank. A lot of flake foods have phosphates in them. Phosphates will feed algae. Also, some foods will have ash. Ash breaks down into phosphates eventually (sort of) and that causes long term phosphate problems. You can switch food now and still battle a phosphate problem for months.
If I was you, I'd take out 10 pounds of crushed coral and replace it with about 15-20 pounds of fine sand. You don't need live sand. The tank is alive and the good bacteria in the tank will spread to the sand in time. Patience. Also, live sand is 3 times as expensive as dry sand. Just use dry sand and it will all be "live" sand in a few months.
Slowly remove the crushed coral. It's just a big sump for all kinds of decaying matter in the tank. Crushed coral holds fish poop, uneaten food and other dead or rotten stuff. In short - crushed coral = BAD for a reef tank. Sand = GOOD for a reef tank.
What type of filtration do you have on the tank right now? If you have a canister filter or a wet dry filter you are kinda working against yourself. Both of those can be used as SUPPLEMENTAL filtration, but are really not the best for your primary filtration system in the tank. Your best bet is using plenty of live rock and a good protein skimmer. IMHO the protein skimmer is the most important part of your filtration system. You can do more with a protein skimmer and a few powerheads than ANY canister filter.
I prefer a more natural filtration system. My little 30g tank has about 4" of fine sand in the tank. I also have a hang on refugium with a skimmer and about 5" of sand. The tank had 60 pounds of live rock in it when I started almost 2yrs ago. As the tank became more stable I was able to remove about 10 pounds of that rock, but I did it slowly and only after the tank was stable for at least 1yr.
The deep sand beds in the tank and refugium provide biological filtration. They are also handling any nitrates. I never test nitrates in my water. I just don't have nitrates. Thats from having 2 deep sand beds.
The skimmer gets rid of any dissolved poop and food in the water column.
The live rock provides biological filtration.
I use a couple powerheads in the tank for water circulation and good gas exchange on the surface of the water.
Thats it. No fancy filter. No canister filter. Nothing complicated. And it works better than 95% of the reefers I've talked too in person and conversed with on the internet, like this forum. I'm always reading threads about people with nitrate problems. Most of them are using a canister filter or a wet-dry filter. 100% of the people with nitrate problems DON'T have a deep sand bed to convert the nitrates into harmless nitrogen gas.
Nitrates are caused by:
Poor water source (tap water)
Poor filtration (canister or wet-dry....... and no DSB)
Poor food quality (loaded with crap your fish aren't going to eat..... but it settles to the bottom and turns into nitrates)
Over-stocking the tank (1" of actual fish body per 10g of water in the tank - MAX)
