[Steven F]

My last time testing then was Dec 30 (a week before the UV filter) and they were
Free FE .25 ppm
Cleated FE .1 ppm
Phos 0-.25ppm

From my own experience making my own fertilizer 0.1ppm chelated is fine how do you measure chelated iron? UV filters are generally bad for chelated iron levels. However your Free FEE might be a problem. If the iron is not chelated it can react with other nutrients forming insoluble iron phosphate, iron borate, or iron molybdate. This can case phsophate, borate, deficiency. Also my observations in my tank and test results has taught me that many test kits cannot tell the different between soluble and insuluble nutrients. But plants generallycan only use soluble nutrients.

When you removed your red root floaters you increased light levels, plant growth rates. And this likely changed nutrient levels and possibly caused nutrient deficiency. When there is a nutrient deficiency plants generally struggle while algae grows rapidly.

while we would all like there to be one or two causes of an algae breakout the drought is that there are likely many different causes. In my tank which has been low tech and high tech at different times hair algae has always been a problem but stag horn,,, I have not seen it.