Why won't ammonia levels go down?

Hello, I just joined this forum, and I have fairly recently got into the aquarium hobby. I have a 29 gallon tank with filter, gravel, live plants, heater, and ornaments. I have had it set up for about a month and a half so far, but since the first 2 weeks the ammonia levels have not budged from 8.0. At first I had 3 small angelfish in there, then I added 3 catfish. The catfish died within 2 more weeks :/ and I then removed all the fish, and did a 100% water change. I have been doing weekly water changes since I got the tank, pouring in Cycle almost everyday @~@ and ammonia remover, ammo-lock, everything! Nothing seems to have an effect on the ammonia. I've tested my tap water, and it is safe, I also have several other smaller tanks which have successfully cycled. I have liquid testers, strip testers, and the stick-on Seachem Ammonia Alert sensor..they all say toxic levels. I'm beginning to think the tank is cursed. Is there any explanation why the ammonia levels won't go down?

Was it used for keeping rats in or anything like that in a previous life?

since you 'll do almost everything to reduce the NH3 level,i say that what is the ammount of pellets that you give to your fishes?after how many days you siphon your water?it may cause due to high wastes from pellets or the wastes from fiishes that is not siphoned yet..

No, no rats or anything was housed in it previously, and over feeding might have helped the ammonia levels, but I did siphon the water once every week.

Welcome to our forum. Whether it's dead plants, dead fish, decayed food, toxic gravel or decorations, toxic chemical additives or toxic cleaners, the ammonia has found its way into your aquarium. Please make sure that nothing in the aquarium is capable of producing large quantities of ammonia. Has someone been adding fish food without your knowledge? With ammonia levels that high, all of the fish should be dead. Maybe you have a false measurement, which can happen with some ammonia detectors especially if you have been using ammonia locking chemicals. Also, Cycle does not contain beneficial bacteria; it just encourages their growth. Some products do contain bacteria, but before you spend lots of money, check for all major sources of ammonia. Once they are eliminated, do a 20 or 30 percent partial water chance every day until the ammonia level stays at zero. You may also want to consider using a reagent type ammonia test kit. Please let me know if any of those ideas helped.

Thanks. I might try some products that have live bacteria in them. So far, the ammonia level hasn't budged from reading highly toxic. No one feeds the fish but me, I took all the fish out, so there's nothing in there now but plants, gravel, and decor.

How long did you let the aquarium cycle? A 29 gallon tank requires at least a month, and adding chemicals does not help the process. In fact, some chemicals may kill the beneficial bacteria needed to make the cycle work. Live plants help the cycling process, and so does adding a small amount of flake food every day. That gives the good bacteria something to eat. Some of our blogs have more details about the nitrogen cycle. Please let me know if some of this helps.

The ammo lock is probably the reason why you are getting high ammonia readings. The ammonia is still present but not in a toxic form i think. Do you know about the nitrogen cycle? If you did the fishless cycle and added ammonia to grow bacteria, the ammonia is still present which is also another reason why. Hope all goes well.