Hi everyone! I was planning to do before and after shots of my tank and this deposit, but of course I didn't remember until I was nearly done. Anyway, I tried the lemon, salt and ice combo on my tank. It started to take the deposit off but just wasn't getting everything. So I used one of those green scrubbers, hot water, my lemon/ice/salt combo and some baking powder (I think that's right- the one that people put in their fridge and sprinkle on stuff to deodarize) and started scrubbing. I was surprised at how quick and easy the calcium deposits went away! Then I would rinse and I could see areas that I hadn't gotten or hadn't gotten well and do those spots again. I rinsed a few times with hot water and then used a paper towel to dry the tank so that no splatters or marks would come up from the washing. Now it looks great and you can't tell there was a huge deposit in the middle of the tank. Now I can see my FBTs and watch what they are up to. As a side note, I used coarse ground sea salt (partly cuz that was what was on hand, partly b/c the larger grains I thought may make a bigger impact. Anyway, I feel much better now that it's clean and that I didn't use anything that could harm them. Thanks for the suggestions everyone!