Old or new algae?


New member
May 15, 2017
Edmond, OK
First time pool owner- I've lowered the CYA into 60-80 range. FCL AND TCL is 10+ held overnight (highest on the strip test). Alk is within range. TH is a little low. The algae won't go away! I've vacuumed twice in the last two days, used Algaecide based on directions... kept the filter on. I'm wondering if the sand doesn't need changed as it may be spitting vacuumed algae out? We purchased this house in September and the pool was a hot mess!


TFP Expert
LifeTime Supporter
Jan 4, 2016
Sydney, NSW, Australia
Pool Size
Salt Water Generator
Welcome to TFP! Good to have you here :)

When I first started out, I gained a lot from this thread: TFPC for Beginners

You'll read about testing, and for Trouble Free Pool Care (TFPC), you'll need a drop-based test kit such as a TF-100 or Taylor K-2006. It's the only option because test strips and pool store testing provide too many incorrect results for reliable pool care.

Your filter won't be able to kill or capture live algae. Only a sanitizer in the water can do that, and chlorine is the most effective sanitizer. The filter will gradually remove the dead algae "carcasses" after they're killed with chlorine. We use a process called a SLAM to completely kill the algae, and then after that it becomes pretty easy to keep the chemistry in range, and your water will be safe and sparkly.

You won't need any algaecides or other expensive chemicals from the pool store, so you'll save back the cost of a test kit very quickly.


TFP Guide
Hello and Welcome to TFP!

For a CYA of 60-80, the shock level to get ahead of the algae is 24-31ppm of chlorine! Much less than that and the algae will find life uncomfortable, but will still multiply and your pool will never clear up. The algaecide is like a bandaid for a kid. It doesn't really do anything except make you feel better. Algaecide doesn't really kill anything and at this point is to little to late.

The only way to test at the high FC levels you need is with a drop based kit.
You may also find the pool cleaning and future maintenance easier if you get the CYA down to the 20/30/40 range.

Bleach is the method we recommend to use to get the chlorine in the pool.
What is your pH? The low end (7.2) is best for this process. But you have to test pH when FC is less than 10ppm
While cleaning your pool, you can ignore and not test for TA and CH.
Backwash when the pressure goes up 25% above clean pressure. You don't need new sand as it doesn't wear out. Your major issue at this point is lack of sufficient chlorine.
Up at the top of the page is PoolMath. Go to that page and familiarize yourself with it. It will calculate the amount of chemicals you need.
Go to Pool School also and read up.
If you take some time to read and ask some questions, you will be able to learn what it takes clean up that pool in no time.