You are going to need to decide on a path forward. Having low building blocks is not what causes dinos to come, it is a lack of other things on surfaces that allow them to gain a foothold. I have P of 1-3 ppb and N of about .1 and I have no appreciable dinos, cyano or diatoms in my tank. However, I have no sterile/new surfaces for them to attach to. Every tank can get a quarter or half-dollar sized patch of something every now and again, but they go as fast as they come and are no problem - there is no way to keep this stuff out of your tank.
By dosing N and P, you are trying to poison them. I am conflicted on if this works long term since you can poison other things too, but those often look small when you just want dinos gone. I can say that you are filling your rock and sand up with phosphate which one day you might wish that you did not. I would strongly contemplate this before you add too much more phosphate.
It seems that like many others, you are paying the price of a sterile tank startup.
You probably need to choose if you want to manage all of this, like you have been, or let nature do it. I strongly suggest the natural route. If you decide to go this way, it is a great long term decision. I would order a small kit of real live rock from Florida or the Pacific, cure it (or whatever), and wait for a month for it to populate the rest of the tank with good stuff. This usually cuts down cycles and the ugly phase to nearly nothing.
If you added too much P already, then you might need to bring it back down so that some of the awesome critters on the rocks can live - some of the inverts, worm, pods, starfish, etc. thrive with N and P closer to NSW levels. Some does not seem to hurt them too much, but you want them to thrive, repopulate and get everywhere.