My old brain has lost a lot of what I learned in chemistry class in the 60s so I did a search on Trisodium Phosphate. Here is an extract from the Wikipedia listing:

"Similar chemicals were once common in laundry and dishwashing detergents, but the phosphate, being a fertilizer, would cause algal blooms in the bodies of water that the drains led to. In the early 1970s the use of phosphate-containing products was limited. Now products sold as TSP Substitute, containing 80–90% sodium carbonate, are promoted as a direct substitute."

Notice what it says about ALGAE---- Richard may want to weigh in, but I would not intentionally put phosphates in my pool.