If you ate changing out 30% twice a week, the nitrates ought to be significantly lower already. If I were concerned with keeping my shrimp berried and carrying those eggs to term, I would stop with the ei dosing , especially the micros and nitrogen so diminish the need for water change. If the shrimp aren't a priority, at the very lease see to the source of the nitrate elevation. Perhaps the soil is leeching it?
"I am Groot", the faithful protector