Tank is dying a slow death! Need some serious help!

I think my problem is my water. Nutrient levels (that I test for) are okay but I waited too long to change out my rodi filters and whatever has been seeping through has killed off my trumpets, birdsnest, and montis. I went for well over a year with virtually no algae growth of any kind. Now I have more bubble algae than I can count and a ton of this red crap. Lights are AI Sols running largely in the blue spectrum, so I don't think its lighting related for me. I just got all new filters for my rodi and plan to do a very large water change sometime in the next few days to see if I can kick things back in gear.