I'm new to the whole fish tank thing. So I bought my fish tank and prepared it filled it with water and used PRIME to make it safe for my fish I then used stability because it was recommended to me to help keep the tank in good shape. I got a few feeder fish for the tank first to make sure it was safe and they lived in it for a night and part of the day. I took my water to get tested and all of the testing came back perfect so I bought a red tiger oscar for my tank and introduced him after 20 minutes so that hed be acclimated to the water. He almost immediately sank to the bottom of the tank and doesn't move around much. The feeders were in the tank with him but he just ignored them. The next day same thing (by this point the feeders had been removed) I tried adding them again but no go. I tried a cricket no interest. I dropped in a shrimp no interest. I have noticed however that when I turn the lights off he moves around. And today he's been moving around more frequently with the ligths on but swimming backwards and jolting around almost like attacking the glass. He's tried going for the feeder but not with too much interest. And then just sinks back down again. What's wrong? And what should I do? He was pretty active at the pet store

I think he's fine, probably just had to get used to the new tank and in a few days will be fine, gl!

Oh and also forgot to mention. He's currently in the tank with a small feeder fish and a ghost shrimp. He's just sitting in the corner looking at them.

Does he look sick???
Maybe just doesn't feel like eating or something... Idk!!!

Looks normal I guess

When I turned off his light he ate the feeder and the shrimp. So I turned on the light and he then started sulking again and he spit up the shrimp whole and alive

When I turned off his light he ate the feeder and the shrimp. So I turned on the light and he then started sulking again and he spit up the shrimp whole and alive. And now when he swims around he takes chomps at the glass

He might just be getting used to the new tank. If he behaves better with the light off then leave it off. How big is this Oscar and how big is the tank? Have you checked the water parameters? It sound like you rushed into putting the Oscar in the tank and I don't think your tank is cycled at this point. That could prove to be a problem. Also, if he is still small then he might not bother with them too much until be gets a little bigger.

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10gal fry tank planted with Wisteria, Java Moss, Anuabis and Anacharis
35gal Sponge Bob tank with live bearing tropicals (daughters tank)
15gal planted with Swords, Java Fern, Wisteria and Red Rubin housing 10 fry and 2 bladder snails
55 gal with Oscar (future planted tank with angels and flowerhorns)
55 gal Community tank (platys, mollys, guppys, glass catfish, angels, phantom tetra, red eye tetra and swordtails)

oscars can just get grumpy, and when they do thats pretty much how they act. i had 3 at one point and two of them picked on the other to the point where he had scratches all over his face. but he was happier (still came to the front of the tank to greet me and ate aggressivly) being left in the tank with the fish picking on him then he was when i moved him to his own 50 gallon (tank was established and all he did was sit in the back corner of the tank and not eat). i have never seen a lone oscar look very happy. i agree with amie, it sounds like u put the fish in way too soon, especially a fish that puts that much of a load on the tank. even if you do fix this problem you will most likely have another problem when the tank turn cloudy and u get your ammonia spike) there are some "bacteria in a bottle" type things that some people say work and some people say dont work, reguardles...... it doesnt hurt) another very helpful tank starting method is to get some gravel out of a established tank and just put it in your tank in a plastic bowl or something. like stated from someone else before..... size of tank and size of fish would be helpful. i recall you saying that they tested the water and it was fine but if u took it to petco or petsmart you can pretty much assuming they dont know what they are talking about. i had some one at petsmart tell me oscars like 8.2 ph the best. so if you have a test kit to test the stuff yourself that would be cool or just take another sample of water in for them to test and just record the numbers they come up with. if you got him from a petstore that keeps their oscars together (like most do) then your fish could just be unhappy about being alone. fish can generally live at least a week without eating and ive had plenty of fish that won't eat for 5 or 6 days after being put in a new tank. ive had ocsars that have lived in 90 degree water for a few days before and nothing bad happened at all. i would suggest putting temp at 78 (unless you have a really big heater, the temp change will not hurt them) i have had incredible luck with aquarium salt so i would suggest the normal dose of that (1 tbs per 5 gallons) i also use prime and stress coat and have never had an issue with either of thoes either so......78 degrees, 1 tbs aquarium salt per 5 gallons, get some bacteria in there, prime, and stress coat.

on another note feeder goldfish are bad and do not have all the stuff needed for a healthy fish, most times bad things happen (example: hole in head), hikari (which seems to be one of the better companies) makes a pretty wide variety to choose from. i used cichlid gold and my fish loved it. Hikari Cichlid Gold Food-8.8 oz - Food - Fish - PetSmart