Need answers to many questions. Please help

First I just want to say you have all been a great help, but for the sake of time and conciseness I will ask you (if you answer these questions) to read my What is going on thread for tank info. I have fixed the problems from that thread and the tank is now running great until today. My last cory, the one who was with me since the beginning of the cycle was found dead with no explanation. My stats as of 5 minutes ago are, 0 amm, -ites, and 5 Nitrates. Temp 79-80 Ph 7.4-7.6 (not quite sure, but I put pics below).

So here are my questions

1. Why did my cory die? Is there a reason? What should I do to help prevent and discover the cause?

2. I have this algae on the bottom of my driftwood. Also algae on tall plants. Should I remove it? What is it? Pics below

3. My amano shrimp are POOPING MACHINES. It's non-stop and an hour after a water change when all the poop was siphoned out, there is a ton there magically. (Pic about a day after WC) How can I prevent this? I am assuming I can't.

4. Because of #3 and small particles in the water, I am almost well past considering and about to purchase a canister filter with a lot more than enough filtration. My choices are a fluval 306 or 406, or a Eheim 2217 or 2215. Which is better? I like Fluval for the ease of cleaning and the media that comes with it, but Eheim is 50$ cheaper and has same reviews plus no water bypass but GREEN HOSES . My aquaclear 50 just isn't cutting it. (not picking up particles)

5. Foamy film on surface? Is it harmful? Explanation or experience anyone?

Thanks for the time you spent reading this. Hoping for some help.

PICTURES HERE

1. Still not sure the cycle killed him.

2. Anymore info? I have algae but none like the one under the driftwood. You didn't exactly answer my question for 2

3. I guess so just really want to know how to not have it collect on sand because it looks bad.

4. As I said in the post look in my previous thread. It's 29 gallons though w/ aquaclear 50

5. Ok, should I be worried or just leave it be?

Thanks

Just a plant. Hygrophillia difformis

Thanks Evil, I am trying to get the plants to grow in more, but it's always a work in progress

Rufloman, I'm not sure if you read my post of replies but I said 29 gallons. If you can restate your lost reply that would be great

Thanks