Lost both Clown Loaches - Need help!

First topic message reminder :

I had bought these from Pet Smart recently. I know they were eating the snails as I have seen them eat. They tended to hide quite often & I would see at least one of them laying on it's side, which they are known for as they "sleep".
I looked in the tank tonight to see one laying on it's side, but the black markings were faded & there was a dark green patch on it's under-side.
I then started looking around for the second one, only to find it's remains on the intake of the big filter. All that was left was the head.
In that tank, I have one large ID shark, 2 baby ID sharks, 2 large common plecos & several Oto cats.

Is it possible that there is something wrong with the snails? Both filters have a bunch of snails in them, so the only real way to get rid of them is to do a complete tear down of that tanks and that is just not possible.The water tests out fine, with a small increase in ammonia. I do 50% water changes and gravel cleans each week as well.
https://2img.net/h/oi59.tinypic.com/2dgm261.jpg

Any ideas as to what this is?

Ok, what I have done is taken my empty shrimp pellet aluminum can, punched a hole in the lid, put a bunch of algae wafers inside it.
I feel this is a losing battle due to the size of the tank, the amount of snails and their size. They are also inside the canister filter & the 10g filter. I have cleaned them out & still they come back.

Being subtle is key. Don't rush it. One or 2 wafers with a plastic water bottle or Something inert. I would avoid all metals in a tank. Metals are usually toxic if they are released into the tank.

I can send you some assassin snails in the spring if you want