If you believe that your substrate is depleted than not dosing anything and doing big water changes will surely deprive the plants more than the algae. It's pretty much impossible to rid the water of all nutrients that algae won't grow. I think there's still some life in the AS after 4 months so I would at least dose K and micros which you would not be getting from the substrate or the tank.
If you started the tank with 8 hours light that would have been a problem, so I would definitely reduce that or if reduce your peak lighting to 2-3 hours and doing regular large water changes.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.