All of a sudden so many replies....
First of all, I am sorry to let you know that while the medicine (Kick ICH) seems working and ich starts to disappear, it also messed up the experiment and after just one dose PO4 raised to 0.15ppm. I read the label and it said nothing about containing PO4, but there is a curious line: "absorbent media should be removed (phosphate absorbents are OK)". That said something.....
Adding fishes to the tank, while sounds good, is not an option since fishes will produce more wastes than it can intake. Also you have no control of the composition of what is produced by the fishes and you cannot just take the fishes out and thrown it away like bacteria/algae......
As I mentioned in previous posts, I would like to use nitrate instead of ammonia but I cannot get pure nitrate in Hong Kong without a license... That said, I am not regretted since the results of using ammonia seems to be much more profound than using nitrate (as reported in another post in this forum).
For now, I would continue the current ammonia dose for the time being, and hope it could help to keep the PO4 load in check. I will keep monitoring and see if I can get a balance in the end...
Thank you for all your advice.