It is my opinion, and I wouldn't take it for much but... you feed way too much food, like on another level overfeed. 6 cubes everyday, no wonder your phosphates are at 0.15, how are you not battling an algae outbreak with all those nutrients in the water, especially with the amount of light on the tank?
You could use the lanthium chloride as suggested, RedSea Nopox, to pull the phosphates down however if and when you stop dosing it you may get a spike in nitrates, as what I understand from my LFS your basically dosing a sugar which target feeds a specific bacteria, if you abruptly stop dosing that newly formed bacteria may begin to die off, hence the spike. However in your case you have a 4 year old tank so I don't know...
Id start out by feeding less, maybe every other day, look at it this way, the fish frenzy when food is introduced is because it is naturally programmed in the fish's head that they don't know when the next meal will be it could even be several days so eat up while you can.. Hopefully this bit gives you something to think about maybe others have input.