Analyze my water readings please

[jsteiert]

I have a 20g tank with 25 lbs LR, 20lbs LS in it. I have 130 watts PC light, a protien skimmer rated for up to a 100g tank, a filter with no media in it, just for water movement, a power head and heater.
Livestock:
2 false percs (about 1" in length each)
1 lawnmower blenny
1 blue linkia star
several turbo snails
several blue leg hermits
1 coral banded shrimp
1 med colony of zenia
1 med colony of orange polyps
1 sm ricordia
2 sm feather dusters
1 branch of gorgonia
several sm mushrooms
This small tank has been a struggle to keep, nitrates are always high, some corals wont live in it at all where others do very nicely, I tried to keep a seabe for my clowns but that did not survive.
Im still in my learning process and sometimes it is painful and expensive. I need some advise and knowledge from the more experianced reefers on this site please.
I just tested my water after a 20% water change last night please give me your thoughts on my readings-
DKH - 6.7
Meq/L-2.4
CA-540
Mg-1455
PH-8.0
Ammonia- 0
Nitrate-20
Nitrite-0
Salinity- 34PPT
Water temp-80.3
I have been using oceanic salt since I started my tank in Oct 05, but after reading thru many posts on here that may not be a wise decision for future water changes.
I do a 20% water change weekly, only feed twice a week. Lights are on a timer with 8 hours run time per day.
I will post some pictures after I download them.
Please give me your opinions.... I want to improve my tank and make it more beautiful than it is now, also with my lighting what types of corals can i keep?
I also have some pictures on the reef board, check them out.

 

[chipmaker]

I would try and get my alk up higher as well as bump up the temp and sg to 1.026 or so. Feed a bit more often, and give lights a 10 hour try. I assume yu have a 50/50 bulb in the light? or at least a 10K?
Certainly nothing wrong with using oceanic salt. Try some 2 part B-ionic calcium / alk or other equal brand. It is about all that I ever use to dose a tank with, and it usually does make things higher in ther ph and alk range.

 

[jsteiert]

For lights I have a 65w 10K and a 65w atinic (spelling?)

 

[hatessushi]

With a calcium level of 540 I would not dose with anything calcium. Calcium is best from 380 to 420. Your temp is fine at 80, I keep mine at 78.5. All of your reading look fine with the exception of the nitrates but even 20 is within tolerence. A water change would help bring it down a bit seeing it's a 20 gal. tank. Since you are keeping corals I would not add anymore fish. The reason being that your tank size is samll and water parameters can change in a very short time making it difficult to keep the water stable. Just keep new water ready at all times just in case and check water frequesntly.