Your current dosing seems about right if you reduce water changes to 25% weekly. Here is what you're currently dosing every other day...
The reason I gave those numbers is so you can model the trends here
. If you know the ranges for non-limiting nutrients you can see your dosing regime will be fine. If you don't know those numbers or are confused about non-limiting nutrients give this a read
Can you reduce your current dosing? Probably. However, I'm not a big fan of approaching nutrient limitation to save a few cents worth of fertilizer. Makes no sense to me. The sweet spot is so large we should never think about reducing levels that low IMO. You're doing enough water changes to eliminate the guess work or testing requirements, hence the original conception of EI.