GDA is a tough cookie, I've tried a lot of different things to eradicate it, even chemically, but I also still have it. There are some things that help marginally, like less light and UV but IMO nutrient ratios or levels don't make any difference. And believe me, I've tried all of them, NO3, PO4, Fe, Ca and Mg in every combination. I can't notice any difference in GDA in N ppm's.
I also have a low light non CO2 tank with T8 bulbs. No GDA there.
You could also start to use the new canister and let the old one run for a few weeks. Then you stop the old one.