Dr. Fish;766507 wrote: The idea is that nitrate and phosphate are both consumed by the bacteria you are trying to proliferate. The stoichiometry of consumption of each compound is not equal in that nitrate is consumed at a faster rate than phosphate, therefore you can be nitrate limited.
So, if you take this into account you can try and skip the use of GFO until you are showing a reading of 0 nitrate and see where your phosphates end up at. If they are above what you like, but nitrates are now at 0 you can resume a small amount of GFO to bring your phosphates back to zero.