clear pool water, tests great still have algae

[GAROB]

I have a sand filter with 2 year old sand. Last year went well. This year, pulling the hair out of my head. We have not been able to use the pool as we would like. The water is crystal clear but alot of algae sitting on the floor. I have backwashed, rinsed, backwashed rinsed and same results. I brought in a sample and all tests were comfortably within range or slightly on the high side (Chlorine). After the last time backwashing, I placed a white sock over the jet and it was green. Why would the filter be sending algae back into the pool?

 

[JohnT]

More than likely your chlorine is too low. Post a full set of test numbers, particularly FC and CYA.

 

[tim5055]

As John has pointed out, you most probably don't have a problem with your filter - you have a problem with your chemicals. Your sand is actually millions of years old and having been in your filter for a couple of years more has not damaged it. Don't let anyone "sell" you a sand exchange. Sand in filters almost never needs changing.

From your comment "I brought in a sample and all tests were comfortably within range or slightly on the high side (Chlorine)" I will deduce that you do not have your own test kit. What the pool stores say is "within range" and what folks here follow are usually two different things.

We want you to learn to take control of your pool and it's testing. To do so you need to arm yourself with the knowledge and tools necessary to care for your pool.

The knowledge is condensed in the Pool School link at the top of every page. It is a great community here, but we do ask that you read and try to understand the information being taught. Questions are always welcome and folks will try to direct you and teach you the methods.

The tools are not limited to the brushes, vacuum hoses and other stuff you use around the pool, but include the most important item - one of the recommended test kits. You can buy a kit at a pool store, but again the pool store kits generally won't cut it. To effectively practice the TFPC methods, the FAS/DPD chlorine test is essential. All these kits contain that test while very few other kits do. Think of it this way, do you see a doctor blindly prescribing drugs without seeing the patient or having tests run? Here at TFP we are going to ask for photos so we can see the condition of the water and are going to ask for a full set of test results.

Additionally, it would help us if you would add the following information to your signature

• The size of your pool in gallons
  
• If your pool is an AG (above ground) or IG (in ground)
  
• If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass
  
• The type of filter you have (sand, DE, cartridge) and, if you know, the brand and model of the filter.
  
• If you know, please tell us the brand and model of the pump, and mention if is it a two speed or variable speed pump.
  
• Date of pool build/install, particularly important if less then a year old.
  
• What kind/model of water test kit you are using
  
• Other significant accessories or options, such as a spa , SWG, or cleaner
  

 

[Patrick_B]

I have a sand filter with 2 year old sand. Last year went well. This year, pulling the hair out of my head. We have not been able to use the pool as we would like. The water is crystal clear but alot of algae sitting on the floor. I have backwashed, rinsed, backwashed rinsed and same results. I brought in a sample and all tests were comfortably within range or slightly on the high side (Chlorine). After the last time backwashing, I placed a white sock over the jet and it was green. Why would the filter be sending algae back into the pool?

Welcome GAROB,

There is one, and only one reason for that. No matter who is telling you what, the reason is a lack of adequate Free Chlorine levels.

To help you help yourself, we need some good hard numbers to correctly assess the problem. We need to know the Cya (Stabilizer) level, and the FC (FREE Chlorine) level. If your test turns Yellow, then it only shows Total Chlorine.

I'm not saying you have one, but this sounds like a classic example of an over stabilized pool. You need Cya in the water to buffer and protect FC, but some sources of FC like Pucks contain Cya. As you use these for Chlorine, you add too much Cya over time, (2 years is more than plenty) and the same FC level no longer does the Job. In other words, you must know the Cya level to know what the proper FC level should be. To get this accurate, you really need your own test kit. Some places test accurately for it, but many do not.

We are all about DIY, Knowledge, and testing our own pools. It really isn't much of a mystery if you are willing to read and learn just a little. Then be willing to do a little testing, at first each day, later maybe less. Once you do this, having a clear, non green, safe pool will be easier than you ever imagined. Almost certainly much cheaper to maintain as well.