Algae again

It has literally been years since I have had any problems with algae but low
and behold I now have a problem. It seemed to occur after I ran out of base
fertiliser (added weekly in tablet form) and just continued to use daily
drops. A film of algae started to form accross the surface of the water. I
siphoned of the algae and recommenced with the base fertiliser. I thought
that the algae must be due to a build up of nutrient from the daily drops as
the plants were not growing to their full capabiliteis due to the cessation
of base fertiliser. With this in mind I have waited a few weeks and have
continued to siphon out the algae but it keeps coming back. Surely my plants
would be back to where they were. The algae is lime green in colour and
forms a matt not dissimular to petrol on water. There is still no algae in
the water column (except for a few small spots to feed the Ottos.). Anyone
else had this experience? Suggestions please. Oh, Iron levels still around
0.1ppm and O Nitrate!