Algae creeps back in through the filter

[erin.frey5319]

b]Problem[/b]: Algae particles are so small they're creeping back into the pool through the filter when I vacuum so I can't get the algae to go away. Is there a trick? We've ensured the filter is clean, we tried to use a bag that is meant to catch the smallest particles and that didn't work. Is the only answer to not use the filter and just reduce the water volume by vacuuming algae right out onto the ground?

FC:10 - very high
TC:10 - very high
pH:7.2 ok
TA:120 ok
CH:
CYA:
Stabilizer is 120 - very high

My pool: Intex 20' round above ground
Pool chemicals: just shocked it, algaecide once a week
My pump & filter: Intex model 635T pump filter
Other info:

[Denniswiseman]

With a CYA of 120 you need a slam level of 48ppm chlorine

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

Get your CYA down to about 40-50 and then do a Slam (Shock Level and Maintain) with relation to Chlorine / CYA Chart and Recommended Pool Levels

Forget about algecide as a properly sanitised pool doesn't need any algecide

You can vacuum to waste to lower your water level which will lower your CYA but you will need to lower it about 2/3rds to get down to about 40 CYA

[Teapot1]

Follow what Dennis says and you wont have any more problems with algae.

[Denniswiseman]

One other thing

Use these common products to balance your pool
Liquid chlorine (sodium hypochlorite or plain bleach)
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

[Lucas Anderson]

To solve the problem, you should use liquid chlorine and install a water filter. But before that, clean your pool to get the best results.