I've been battling high nitrates in the tank (I think due to excess organics which I've now cleaned up) but now it appears to be under control (5-10ppm). Because of the high nitrate and slow growth, I was only dosing a 1/2 thrive dose per week because I'm trying to prevent algae breakouts from occurring. I figured the slow growth meant the plants weren't using much nutrients so didn't want to over fertilize. Now I'm wondering if limiting my dosing is what's caused the slow growth. I'm not seeing any obvious signs of deficiency in the growth, just slow.
So how do I know when I need to dose more for the plants, vs dose less to not overload the system and cause algae? Currently I only see a little green alage on some driftwood and otherwise just diatoms on my SR and some slower growing rotala stems.
What was the NO3 reading when you considered it "high"?? Most with "Dutch" type tanks keep it quite a bit higher than that. Remember, the more light and more CO2 you provide the higher need for nutrients.
At 5 - 10 ppm NO3 my tank would hate me. Plants would be stalled, in poor health, and a target for algae. Strong well fed plants are easily the best defense against algae.
You also make an assumption that more ferts will cause algae. That has not been my experience, or the experience of many others in the hobby. IMO, too few ferts is much more likely to bring on algae than too many. Think providing plants all they need, not defeating algae.
As to your dosing level, I have no idea as you don't say what size your "dose" of Thrive is. And most people won't take the time to look it up and try to figure it out. You are better off starting to think in terms of ppm of NO3/PO4/K.....and micros too. It's the universal language, and will help people help you.
As to slow growth, if plants are healthy I would not be to worried about the growth rate.
Any pics of the tank? A picture is worth a thousand words and again will help others help you.