Don't add CYA, till the pool is no longer green -- algal biofims can incorporate bacteria that metabolize CYA to ammonia or worse. Since you have some CYA, go ahead and add plain 6% household bleach at the rate of 3 gallons per dose till you read the "orange" level on an OTO (yellow drops) kit. Hold your chlorine level there until you get a K2006, and can accurately test both chlorine and CYA levels.

Check your pH BEFORE the chlorine gets that high and adjust it to between 7.0 and 8.0. Use 20 Mule Team borax to raise; muriatic acid (see page link in my signature) to lower.

Put your sand filter on recirculate -- it won't filter that stuff and we're beginning to think those undersized over-driven AG sand filters actually fragment algal particles into an even finer and harder-to-filter slurry.

Read the test kit, muriatic acid, and Best Guess pages in my signature -- they all apply.

Just curious -- nothing to do with pools -- are you at Lejeune?