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Where most of the fish that died small fry or babies guppies?
I think RubberFrog is onto something possibly with the anchor worm idea (I love that disease site, by the way! Have been using it for about a month now, comes in handy) or maybe even Hydra as a secondary guess. They are common in freshwater in the US and are known to eat fry so I believe the thinking is that they are found most often in livebearers or easily bred fish tanks. You can treat both pretty easily with a anti-parisite med (shouldnt even take that much of it, maybe just a half dose to start) for the anchor worms and the addition of one tablespoon of salt will ruin any hydra's day in a heartbeat. Hydra would be an especially likely problem for people who overstock a tank or do not clean the tank well. How many fish did/do you have in your tank and what is your maintenance routine? Also, do you know what type of algea eater you have exactly?
I believe there are a few other possibilities as well but some are not bad for your tank at all and can be a good source of food for your smaller fish or fry. Others may have some good input for you so keep checking in once in a while. | 
Help! Worms in my tank? 
