i have three oscars in my tank 150 gallon with sand. i have one slgae eater in the tank with them they are about eight inches long each. they just lay at the bottom of my tank they are not eatting i don't know what to do. i feed them pellets, blood worms and feeder fish. what could be wrong. they have been like this for about three weeks.

i do a 15 to 20 % water change every week. the water test is as follows

Ph= 7.6
high range ph= 7.4
nitrate no2 = 5.0
ammonia= 0
nitrate no3 = 40

any advice, please help......
here is a picture of the tank not a very good one though

I think your readings are high.
I'd start with bigger waterchanges (50%) to get your nitrates down.
If your nitrites are indeed 5 your fish are dead allready...
Please retest that, cuz a reading above 2 is deadly.
Do you use a liquid testkit? they're more aqurate then teststrips.

i have both test kits did a quick test this morning i will retest when i get home from work. how often should i do a water change. is there anything that can help me get nitrates down
??????

Nope, just large and regular waterchanges will help.
Did anything happen to the filter, that may have disrupted your Beneficial bacteria?
Like cleaning the filter?

no.. could it be the feeder fish making them just lay around also?

Where the feeder fish quarantined properly?
If not they could transfer disease very easily.
IMHO feeding live feeders is not nescesary to keep your O's healthy.
The amount of food you feed to your fish, will affect your testreadings as well.

i put my feeders in a 10gallon tank before giving them to the fish
how can i quarantine them?

what is best to feed oscars.
??????????

By putting them in a 10Gallon tank before giving them to the fish!lol
Keep 'em separated for a few weeks,and check if they stay healthy before feeding them to your fish.
lots of info on what to feed your Oscar:
www.oscarfishlover.com/oscar-fish-food