Why are all of my clams dying???

[doch]

Yes, I dose Iodine... I don't test for it, but I does the 'beginner amount' that is stated on the bottle... this on top of my weekly water changes. I do feed phyto on occasion... maybe a bottle every month or so... just kind of when I happen to remember to pick it up. I also dose KZ sponge power. ALang, I'm waiting on the same shipment, and in the same boat! I'm thinking that my tank in Fort Mac will be a better clam tank anyways. I can actually see past the penant on the top to see the clams glow. In Edmonton my fixture is so big I can't see anything from the top except during water changes.