tanks dont need window light, best to move it or cover window ( which no one wants to do) , your best bet if you dont want to move a 125 gallon tank is cover the window- sorry- algea can be trouble. how many lumens are you running , you have a deep tank and if you want live plants you need good lighting - your issue is most likely the window though.keep the algea scraped off the glass, otocinclus are good algea eaters, aquaponic culture of plants help, pothos works well, so will other moisture loving plants- I have heard of some folk using strawberry plants! I have a 90 gallon that sits in the middlle of my living room not near windows, 216 lumens for plant growth, I use pothos arrowhead plant as aquaculture, have otocinclus as well as amano shrimp,clown pleco. I still get growth on glass but no real problem. hope that helps, NOW if you get a pleco you MUST have driftwood for them as they eat driftwood. there is a company called Repashy ( internet sales only) that has superb food for plecos. beware of plecos some get huge, some stay small.read up on them very well before you make your choice. another cause of algea can be overfeeding but we dont want you to starve your fish!!!! so , see if any of this helps