Fish slowly dying, plants not growing

[dohara1985]

To begin thanks in advance for any and all help. First let me explain the issue and than I will give some background information. My 7 plants, Basic tomato, an established big boy tomato up rooted from soil outside, green pepper and 4 strawberries, are all dying except for a very small amount of new growth. All the plants, except the big boy, were all bought at Walmart about a month ago. The Pepper plant had a small pepper on it. it has not grown at all. most the leaves on all plants are wilting. Not showing any other signs of issues. i.e. yellow or black leaves, color change, or spots.

Ok so a little background. About 10 months ago I started a system. I started with about 2 dozen gold fish in my 40 gal tank. It is a basic flood and flow system using fish gravel as the medium. I tried several other systems before this but for different reasons none of them worked for my situation. Anyways most of the goldfish died pretty quick. only about 6 survived and grew pretty quick. I tried several different plants. Egg plants, tomatoes, strawberries, peppers, lettuce. Some from seeds and other from store bought plants. It was weird, none of them grew. they just stayed the same for months. one by one, weeks apart, a plant would just die immediately with no warning. Suddenly and with in hours would go from a full plant to literally nothing. The other plants would be fine for awhile. Eventually the last plant died. None of the plants ever produced fruit or grew. I eventually added a small frog and a sucker fish to help the cloudyness of the tank. That part worked well. After all the plants died I stopped flowing the water and let the tank be. The water got very cloudy. About a month ago I dumped the fish pebbles out and got expanded clay pebbles. I also bought 20 fish. 12 of them were small gold fish and the other 8 were a tetra. All of the tetras died pretty quick and about half the new goldfish including yesterday my biggest goldfish from the previous batch 10 months ago. He was about 8 inches long, kinda sad.

Because of goldy dying I am jumping into action. Since starting the system I have done a lot of research but am constantly getting mixed messages and having a hard time getting my system working.

With the first system I had the flood and flow on a 30 min on 1 hr off interval. I have read a lot of disagreeing info on how long to have it on/off. I currently have it set to 30 min on and a hr and a half off.

The lights I am using are led bulbs. 6 of them are small about 20 watts and I have one large one about 60 watts if I remember correctly. They are currently on a timer for 12 hours on/off. I have tried adjusting the height several times with no noticeable changes to the plants.

I am stumped. The fish don't seem to have any visible issues and they are definitely not sluggish. I do feed them a lot, three or four times a day, but the cycle seems to be working well. The plants just don't seem to be growing or absorbing the nitrate. A lot of forums suggest to add more plants but if the ones I have are wilting and not growing I don't see how adding more plants could possibly make things better.

ammonia seems to be about 0.25
Nitrate at least 200
Nitrite about .5
Hardness very hard
moderate alkalinity
ph about 6.8

Any help would be much appreciated!!!!!!!!!!!!!!