Back washing sand filter caused algea in pool

[da2434890]

When I was gone over the summer the person who maintained the pool had green algae build up in the pool that is normally chlorinated with a SWG. He put powdered chlorine to shock the pool and get rid of the algae. This seemed to work but he did say that the pool appeared cloudy after he back washed the sand filter.

Now about three weeks later the pool seems to be getting just a little green and we had some winds that caused more sand to blow into the pool. So, first I also put in powdered chlorine to shock the pool. Then two days later I used a normal hose and vacuum attached to the skimmer suction (instead of my Kreepy Krauly which does a so-so job) and got the pool looking really good. Since I knew I had vacuumed up a lot of sand I then back washed the sand filter for 5 to 10 minutes until after I was not seeing anything in the visible glass and then ran it on rinse for about 30 to 45 seconds. Within about 15 minutes the pool was much greener than ever.

To complicate things I live directly on the Sea of Cortez which is 4 times saltier than the normal ocean. Rain in the desert is almost non-existent and vegetation is very minimal. Thus, the pool only gets very fine sand blowing in and only rarely a few grass clipping and/or flowers. However, the sun is very intense and the temperature is 90 during the day and 80 at night so the pool temperature is currently about 90 degrees F.

Also to complicate things I discovered that my R13 for testing CYA was used up over the summer so I will try to go to a friends today to hopefully get it tested. When tested in July the CYA was 65. Other readings are:
FC 2 I try to keep it about this for the SWG
PH 7.2 I try to keep it low because of the extremely high calcium
TA 70
CYA ???
CH 600 Yes, extremely high but so is the water from the tap. I had looked into means of trying to lower the CH but have not found anything. The companies who do this in AZ are not interested in coming down to San Carlos even though I think it would be a good business opportunity for them.

Because of the high CH I typically have to clean the scale buildup on the Pentair IC40 SWG about every 3 weeks. This is a real pain since it typically takes many acid washes and hours to do. This is probably why the algae reappeared.

Now, I am out of powdered chlorine so last night I purchased some Chlorox to cure the algae. I tried to purchase more chlorine locally but the pool store ?? did not have any. Basically, the nearest pool store is 300 miles away in Tucson.

I am thinking that I should add the chlorox directly into the skimmer with only the skimmer valve open and give the sand filter a good sanitation this way. The chlorox obviously would then go directly into the pool and kill the algae. When the water is again clear I would think that again I would need to back wash the sand filter. Does this make sense or is there something else I am missing.

I am also thinking that a robotic cleaner makes sense because then the dirt is going into its bag and not the sand filter. Besides, the Kreepy Krauly takes at least 4 hours and still misses areas, does not do the ledge to sit on or the infinity pool, and frequently gets stuck on the stairs.

 

[duraleigh]

Well, your thoughts are on the right track but you are blaming the wrong culprit. Your filter had nothing to do with the algae growing.....it was the lack of chlorine that let algae grow. Based on what you posted, I think you sort of know that already.

What you need to do is shock your pool. Do you have a test kit so you can post test results?......that's the first step.

You can use common household bleach found in the grocery store and it is better than any powdered chlorine you have been using. Possibly less expensive, too.

 

[da2434890]

I agree that the original cause was the lack of chlorine. However, after adding chlorine and having the pool clear and then back washing why did the pool again get green in 15 minutes? Or what can be done to get the algae out of the sand filter if back washing and rinsing did not do the job? I don't want to use the bleach and have this happen again.

Note, the test readings are in the original post with the exception of CYA. I am still trying to find someone who has the chemicals to do the test.

 

[JohnT]

Algae can't grow in the filter. It requires sunlight, so you will only have algae in the filter if you have algae in the pool.

 

[da2434890]

I know that the lack of chlorine was the cause of the green water and that it did not grow in the filter. What I do not understand is that is acted like the algae was trapped in the filter and it all was pumped back into the pool after the filter was back washed and then rinsed. I am wondering if the filter has an issue or if something I did was wrong causing the green algae to reappear in the pool in only 15 minutes after cleaning and switched back to the normal mode.

 

[da2434890]

Hayward says the problem is I need to do what is called floculation or floc. The problem is that a sand filter cannot remove small particles and the dead algae is a small particle. What floc does is makes the small particles stick together getting large enough particles so that the sand filter removes them. The product to use is called alum and is sold under many names. Or, maybe this is a really good reason to have a DE filter and not a sand filter. My temporary solution is to use my small hand held vacuum that has a very fine filter and slowly clean the pool.

 

[JohnT]

Hayward says the problem is I need to do what is called floculation or floc. The problem is that a sand filter cannot remove small particles and the dead algae is a small particle. What floc does is makes the small particles stick together getting large enough particles so that the sand filter removes them. The product to use is called alum and is sold under many names. Or, maybe this is a really good reason to have a DE filter and not a sand filter. My temporary solution is to use my small hand held vacuum that has a very fine filter and slowly clean the pool.

Hayward is wrong. You don't need floc. Dead algae is brown or gray. Live algae is green. You don't need a DE filter.

Algae is 100% a chemical problem and 0% a filter problem.

 

[duraleigh]

da,

Yes, Hayward is wrong. You can get a better grasp of pool water chemistry by reading ABC's of Pool Water Chemistry in Pool School. As John said, your issue is all chemistry related and has nothing to do with your filter.

 

[da2434890]

Hayward was correct. The algae was already killed and the sand filter could not remove particles this small. Using a floc to make the particles large, letting it settle, and then vacuuming to waste made the water clear. Yes, proper chemicals would have prevented the situation but shocking had already been done when my first post was made. I hope that this helps others with a similar situation.

 

[teapot]

I then back washed the sand filter for 5 to 10 minutes until after I was not seeing anything in the visible glass and then ran it on rinse for about 30 to 45 seconds.

That's a long backwash, nothing wrong with that if it's needed but it will have lifted the sand bed and loosened the entire filter. 45 second was not long enough to re settle the sand and compact it ready to start filtering. I have lost count of how many swamps I have brought back to life without needing any floc, just using sand (of the correct grade) will easily filter out the dead algae, floc just speeds the process up but you need to backwash the filter afterwards as even dead algae can become food for other bacteria if your chlorine level drops.

Haywards advice is questionable and typical of a company supporting the industry (helping to make sales)

In future backwash for less time and rinse for much longer, they both expel water to waste but will compress the sand into the correct position for filtering, it's a common mistake.

 

[duraleigh]

Just as a clarification to others reading this thread, Any filter will filter adequately enough to remove dead algae. Sand, DE or a cartridge are all capable of that.....it is done weekly by thousands of pool owners who experience an algae outbreak.

I am not sure why a Hayward representative would say it won't but, nevertheless, it is incorrect.

 

[PoolGuyNJ]

I would also add that if the algae bloom was significant, initially vacuuming to waste would get rid of the majority of dead stuff and not gunk up a filter. Yes, it will wind up diluting things like salt, CYA, and calcium, but it's faster and easier than degunking the filter.

Scott

 

[seeclearly]

Having a somewhat similar problem (curing algae outbreak). I have never used the Rinse setting on my sand filter. When do you use it? Are the valves set the same way as for backwash?

Sounds like the idea here is to backwash until water runs clear (5 min or less), then rinse for 5 minutes?

 

[duraleigh]

seeclearly,

From Pool School in the upper right corner of the page....

Sand filters will have either a push/pull main valve or a multiple position valve (multiport) for cleaning the debris trapped by the sand. Whenever changing the position on the main valve, you MUST have the pump off or you will break something. First make sure that any valve on the discharge/waste line is open and any discharge hose is attached and rolled out to where you want the dirty water to go. After turning off the pump, move the lever to the "BACKWASH" position and restart the pump. Most multis have a view glass so that you can see the debris coming out of the filter, other filters will have a section of transparent pipe on the backwash line. The water will run clear for a moment, then get dirty, and finally run clear again. When the water in the glass is ~ clear, turn off the pump. If you have a multiport valve with a "RINSE" setting, switch the multiport to "RINSE", otherwise switch to "FILTER", and run the pump for about 15 seconds. Repeat the backwash cycle. Finally, reposition the valve back to the normal "FILTER" position, and you're all set until the unit needs to be cleaned again. Please note that this process removes water from the pool, so be sure to keep an eye on the water level and don't start the cleaning process if the water is already low!

In my case, I simply run (after backwash and a fairly clear sight glass) in the rinse position for about a minute (plus or minus). It resettles the sand so you don't get a large plume of debris back into your pool after the backwash.