The way I understand it is that with the Nitrate/Molybdenum additive, you should only use it to achieve a ratio of 100:1 in regards to N03 & P04. Based on your previous mention, you should not have to use the solution since your at that range or better. (20ppm:0.15ppm)I was curious when people were adding the nitrate solution how much they were adding per week.
Are you using GFO? You should stop if you are since GFO binds molybdenum which the chaeto needs.
Another question is are you dosing the iron & manganese additive on a daily basis?
If your chaeto is brittle, try dosing a Boron additive.