Answer to #1:
I don't think there is any set rule on how much zucinni to feed a specific pleco size. You kinda just, throw a round in, and haul it out the next day after the pleco has had his fill. Never leave fresh food in your tank for long, it rots fast and can make a tank really really dirty.
Answer to #2:
There isn't any difference between algae disk or waffer except the name. Different brands call their stuff differnt things, ie Wardly Algae Waffers and Hikari Algae Disks. The important thing is to make sure the first ingrediant is spirulina. Only the Wardly Algae Waffers (or disks whatever) have spirulina listed first. Even algae flakes don't have that. I give my goldfish the Wardly stuff now and again, and they like it.
For a Pleco, I usually feed them two waffers depending upon the size of the fish and how fast they clean it up. All uneaten waffer (aka disks) should be scooped out of the tank as quickly as possible. They get all fungused and yucky within 24hrs of sitting in a tank uneaten.
Good luck.
~~Colesea
