Help with algae please.

[bkfit3636]

Problem: I have algae in the pool I have been fighting with low chlorine for about a month now. Got samples done at local pool store they tell me everything is fine just the chlorine. But I know my cya is high and the alkalinity was high till I added muriatic acid today bringing ph from 7.7 to 7.4. I added 25lbs of shock yet still no chlorine. I have done this last Thursday and Friday as well with the shock. Again they tell me the cya I shouldn’t worry about even though I know normally it should be at 30-50ppm and a max of 100ppm. Please any suggestions of insights would help. Looking for other opinions thank you

FC: .11
TC: .22
pH: 7.4
TA: 140
CH: 286
CYA: 175

My pool: 85,000 gallon plaster in-ground
Pool chemicals: Variety
My pump & filter: Sand filter
Other info:

[Teapot1]

Honestly, if it were me I would do a 2/3rds drain and water replace. 25lbs of shock just increases your CYA even more, Stop and change to unstablilised chlorine

[Denniswiseman]

Seconded
Excessive CYA renders your chlorine ineffective and you have to use more to get the same sanitation
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm
To reduce your CYA you have to do a partial drain and refill
Continuous use of Trichlor/Dichlor will raise your CYA which means you have to raise your chlorine level as well

Use these common products to balance your pool
Liquid chlorine (sodium hypochlorite or plain bleach) Liquid chlorine only adds salt
Muriatic acid (hydrochloric acid) to lower pH and TA
Bicarbonate of soda to raise TA
Aeration will raise pH only
Soda ash will raise pH and TA