Whether caustic (NaOH) can be used as pH booster in HP dosing in place of TSP?

Caustic can be used in HP dozing, but not in place of TSP. Rather it can be used along with TSP. If for some reason, your boiler pH is going down, but your phosphate level is ok, then one can use Caustic to increase the Na:PO4 molar ratio. Only thing is that you must check the M and P alkalinity of Boiler Water and maintain it less than equal to 0