The pond can look great, but still be toxic to the fish. The ammonia is too high. As stated, it should never be more than zero, as should nitrite.
You need more filtration and/or maybe fewer fish. More ammonia is being produced than your filtration can handle. Either that, or if the pond is new, the beneficial bacteria have not yet gotten established enough to deal with that amount of ammonia.
I have two canister filters and one large uv light. I think i have too many fish.About 30 fish of sizes from 1/2" to 2". The pond has about 750 Gal.I know from this forum that ammonia comes from un eaten food,poop and urine. So by vacuuming the bottom of the pond twice a year doesn’t that remove the ammonia problem ?
Ammonia is also a product of the fish breathing. So no, vacuuming the bottom of the pond will not help. It might reduce it if you vacuumed every day, but as long as the fish are alive, there will be ammonia.
The beneficial bacteria in your filtration system, or on hard surfaces in your pond, is what keeps the ammonia in check, converting the ammonia to nitrite, and converting that to nitrate. That is the nitrogen cycle and it is constant and never stops. So having sufficient bacteria and filtration is critical.
What kind of fish do you have? And how much filtration are your canister filters rated for? It's normal for that amount to be overrated, or rated for a pond with no fish in it. It's always good to have way more filtration than what is rated for the size of your pond. The more, the better.
Is your pond new? If so, the bacteria may not have had time to grow enough to handle the amount of ammonia in your pond.
Please read about the nitrogen cycle and you will get a better understanding of the process and what is needed for a healthy pond.
Those products do not contain the type of bacteria you need. Those are made for removing sludge, not cycling a pond. The type you need will not survive being bottled or dried or processed and packaged to sit on a shelf. They need air, food (ammonia), the right temperature and water to live.
You can use Prime to bind the ammonia so it won't be available to harm the fish. But for that purpose, it lasts only 48 hours, so you will have to dose it again every 2 days until your filtration system catches up, if this is a new pond. If it has been up and running for a while, you don't have enough filtration for the fish load.