Why don't you do some experimenting to find out what dosages you need, when dosed 3X per week? You can start with the EI method tables, to see what a for certain non-limiting dosage makes the plants do. Then reduce the nitrate dosage a small amount, say 25%, and watch the plants for a week or two to see if anything changes for the worse. If it seems to have no effect, repeat, until you can see a change. Then go back to the previous dosage, and that will be your minimum for nitrates. Repeat this for phosphates. Then repeat it for the trace element mix. If you dose potassium sulfate, do that right after the nitrate reduction.
Now that you know what the minimum dosages are, you can use that, and wait at least 2 weeks between water changes, maybe even a month.