Pool => 17K gallons, PF = 7
1. Kill the algae, first. DE filters don't do well with live algae.
2. Add 6 gallons of plain 6% household bleach, tonight. Pour it around the pool. (Bleach splatters: wear shorts, or pants you don't like!)
3. Buy a cheap OTO / phenol red kit, and order a K-2006 (See test kit info page in link)
4. Buy some DE, like this:
Diatomaceous Earth Pool Filter D.E. 25 lbs @ Amazon



You can order from Amazon, but get at least 10# locally if you can - should be enough for at least one filter load.
5. Do NOT start your filter till the algae is dead. If you can bypass the filter, or lift out the internals, run the pump WITHOUT the filter.
6. Keep adding 6 gallons of bleach each EVENING, till the algae is dead. (blue / gray => no green, even when you brush the bottom.)
7. Test the pH in the evening BEFORE adding bleach (high chlorine screws up phenol red tests). If the pH is above 8.0, add muriatic acid, about 1/2 gallon at a time.
see Using-Muriatic-Acid-to-Safely-Lower-Your-Pools-pH
8. If the pH is below 7.0, add 20 Mule Team Borax, 2 boxes at a time, SLOWLY to the skimmer, with the pump running.

Let us know what happens. Report test results as soon as you get the K-2006