Well, I'm not really a fan of PPS, primarily because that system is founded on three basic principles that have proven to be totally false:
The first false principle is:
That nutrients cause algae. Algae really do not care what the nutrient levels of the tank are. When both plants and algae are in a tank the algae respond to the health of the plants. If the plants are healthy then algae do not interfere. If the plants are unhealthy then this triggers algal blooms.
The second false principle is:
That NO3/PO4 are toxic to fish. The level of toxicity for NO3 is a very high number that we never reach in our dosing. What is much more toxic to fish is the organic pollution that we exacerbate when we fail to keep the tank clean. Doing large frequent water changes rids the tank of pollution. Chronic levels of organic pollution results in bacterial action that produces toxic ammonia and Nitrite and robs the tank of Oxygen. This is what kills the fauna. The NO3 levels that result is simply the smoking gun. When we add the inorganic form of NO3, such as with KNO3 there is no bacterial action associated with it. The higher the NO3 levels the better the plant health. So high Nitrate actually helps to reduce the possibility of algal blooms.
The third false principle is:
That you can manage the nutrient levels using test kits.
There is no way this can be accomplished, because test kits are a grand illusion. Even with expensive ion probe devices. This happens because the test reagents respond to other chemicals in the water that have similar electrochemical signatures of NO3, or NH3 or PO4. Ion probes can be similarly fooled. So for example, if Chloride (Cl-) is in the water, it mimics NO3. The reagents or probes are unable to distinguish between Cl-, NO3- and a host of other ions, so measurements return a high value for NO3. Since you cannot control the level of Cl-, and since it varies daily, you can take readings on ten different occasions and get ten different readings - even if the NO3 levels have not changed during those ten samples.
So because of these factors, it becomes impossible to manage the dosing. It is completely unnecessary to keep nutrient values between some arbitrary set of values and what happens in most cases is that the test kit reads a false high value, the hobbyists takes action by reducing the dosing levels in response, the real nutrient values fall
below the minimum required for those environmental conditions, the plant health fails and algal blooms are incurred. The hobbyist then blames high nutrient levels for this failure.
This scenario happens every day and has been happening for decades, until it was demonstrated that the three principles were false and that the situation was actually the reverse of what people thought. The idea should be therefore to prevent malnutrition and that is most effectively done by consistently dosing a prescribed amount.
Suggested reading:
Why dont nutrients cause algae? | UK Aquatic Plant Society
Do excess nutrients = algae? Is it possible to "know"? | UK Aquatic Plant Society
EI DOSING USING DRY SALTS | UK Aquatic Plant Society
ferts causing high nitrate! | UK Aquatic Plant Society
Cheers,