Drain & Fill for Algae?

Good Afternoon. I've been looking around in the forums, hoping to find the answers I need, because I'm sure they are there, and I hate to ask the same question that has probably been asked hundreds of times! The problem is I don't have the readings like others have, so can't share that information.

I recently had a sand filter change, first one since I bought the house seven years ago. I was assured that would fix my algae problem. It didn't. Now I'm being told that because my pool is over-stabilized, I will need to drain it at least half way and refill it. The only readings I have are what they told me when I took the water in to get tested:

Chlorine - 5
PH 7.6
Alkalinity 120
and Stabilizer is well over 100

Since I don't know what all the abbreviations are in the other posts, I don't know how to compare this to others' problems. I've always just tested chlorine and ph, and my kit shows them both within the color range they are supposed to be.

I'm feeling like a pretty ignorant pool owner, but this is the first time I've had any real issue with it. I hate to put out another couple hundred dollars on a water bill when I just did that for the new sand.

Thanks in advance for any help you can give!

Hello, and welcome to the forum.

I hate to tell you this, but changing the sand isn't going to do anything for the recurring algae problem. Unless it's been a total SWAMP or you're converting from Bacquacil or have some other goop in the filter, the sand really never needs changing. All 4 of the mods on this forum have sand filters....and at least two of us have been using the same sand for over 10 years!!
In looking at your test results, I'd be willing to bet that you either have an inline chlorine feeder and have been using pucks all these years for a chlorine source, or have been using dichlor powder to chlorinate and/or shock. The results that you report, as well as the constant algae problems are consistent with somebody who doesn't realize that as stabilizer (CYA) rises, so must your base chlorine levels. (That's something the pool stores won't tell you, because if you know how to keep a clean, clear pool, they don't make any money!!)

It is possible to run a high stabilizer pool by simply adjusting your chlorine levels upward, once you get the pool cleared. The other option, if water replacement is not an issue for you, is to drain/refill some of the water in the pool to lower the CYA.

Either way, you're gonna need a good test kit. We recommend the K-2006 or K-2006C (same kit, just larger reagent sizes in the C version). If you buy it through the Amazon link in my signature, the Pool Forum makes a little money on the sale which helps us keep this form online. Only buy if the seller is Amato Industries, however. Some other sellers are substituting the K-2005 which you do NOT want. If Amato isn't listed, wait a day or two and try again. They seem to restock pretty quickly when they sell out. I know it's an added expense, but believe me, it's the key to getting your pool back under control.

If you'll tell us what kind of pool (plaster, vinyl, gunite, etc) and the volume, as well as what the water looks like, and what chemicals you've used (need ingredients, not just "shock" or other brand names), we can get you headed in the right direction.