Normally, for a DE filter, rinsing the grids/fingers off with water is sufficient. If there is stuff that won't come off with just water you can soak them in detergent. Ideally, for that, you want to use TSP (trisodium phosphate), but that is often difficult to find. The best alternative is automatic dish washer detergent. Typically you use one cup of TSP/detergent in a garbage pail of water and allow to soak overnight, then rinse off.
Did you use REAL trisodium phosphate or the TSP substitute that is sold in many localities today? If you used a substitute then try soaking them in automatic dishwasher powder such as cascade or electrosol. Use one cup per every 5 gallons of water and soak for at least one hour to overnight, use a soft brush to carefully scrub the grids if anything is sticking to them and then hose them off. If they are showing calcium or metal stains after that then soak them in a dilute muriatic acid solution for about 20-30 minutes or until the bubbling stops. Use 1 cup acid to every 5 gallons of water. Next time you soak you can add the acid and dishwasher detergent or TSP at the same time and only soak once! You can also use a commercial acid based cleaner but it really doesn't work any better or faster and will cost you a lot more to use!
i hate to say it but i use acid although it is not recommend by the manufacture i do it anyway and they come out white and looking good
what i do is take a garbage can fill it with water pour the acid in and leave the nest to soak overnite give it a good rinse in the morning and put it all back together
remember be careful with the acid
i do know that is not the best thing for the filter so try not to kill me over this pratice
it will work
Yes, you did not use TSP (which stands for Tri Sodium Phosphate) but a different chemical, most likely sodium carbonate, which is not as effective a degreaser! (It's the same chemical used in pH increaser, just washing soda AKA soda ash or sal soda!) Try soaking in automatic dishwasher detergent like I suggested above. TSP CANNOT be phosphate free! You used a TSP substitute! If after soaking there is still staining or scale then use the acid as I suggested above. Be aware that acid washing can shorten the lifespan of the grids but it it necessary at times! Just remember to degrease before you acid wash or to combine them as I suggested above.