Backwashing every three days - what's wrong?

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mbowers104

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Jul 2, 2012
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This is an IG pool with a sand filter, used by homeowners in a residential subdivision (I'm the new HOA president). 30' x 50' and approx. 39,000 gallons.

The filter and sand are new this year.

After we backwash, the pressure drops to 18 PSI and stays there for about 3 days. By the fourth day, it has spiked to 30+ PSI, flow slows and we backwash. I know this isn't right and the pool service tech seems as puzzled as I am.

Skimmers and strainer are cleaned regularly.

Any ideas?
 
Yes. Your filter is filtering debris (most likely dead algae) from the water....as it is supposed to do.

You almost surely need to shock the pool. Posting a full set of test results is the first step.
 
How does the water look? Is it cloudy? You are probably on the verge of an algae bloom. Post a complete set of current test results and perform an overnight free chlorine loss test to see if you need to begin the shock process.
 
It's a Pentair Triton C, TRC 140, 36" Heavy Duty Commercial sand filter.

We have been having trouble keeping the free chlorine level in the proper range. I'll get the readings and post them later today.

Thanks.
 
If it helps any, I take care of the pool for a large townhome community, so I know it can be frustrating to deal with. I don't know about you, but today the high here is supposed to be 100° with about a 75° dew point, so we get HEAVY bather loads every day. Right now, I am not having ANY problems, and that's to the credit of the wonderful folks here.

So, I am by no means an expert, but yes, especially if you're having trouble holding FC levels, it's most likely time to shock. Do you know what your CC level is (measured by doing the FC and TC tests and subtracting to get the difference)? I am finding I have to shock our pool at least every other week, but when we have a hot streak where it's 95-100° every day, I have to do it weekly. And I end up backwashing a lot more.

Keep us posted and we'll help you!
 
It's a salt water system. One meter reads 3000 and the other is 2800. I'm told this is the bottom end of acceptable. The system indicates that it is generating chlorine. No warning lights.

Readings this morning: Chlorine: 3; pH: 7.6; Alk: 90.

The water looks a little cloudy.

I'll see if I can find the TC level. I haven't seen that on the daily report.

This is especially frustrating since we pay a pool service to take care of this stuff for us.
 
CYA is 20, which I learned from reading other posts, is low. 30 -50 is recommended. I'll get some and add it.

Not sure what CH is. Calcium Hardness? It doesn't seem to be measured by our pool service.

By the way, thanks for the good advice. I've learned a lot just today and will keep you posted on my progress.
 
I would suggest 40-50ppm CYA in that pool.

BTW, it is more than 39k if it has a deep end and your measurements are correct.

CH is calcium hardness and, while it is a stable parameter, it is also quite important.

read "The ABC's of Pool Water Chemistry" up in Pool School
 

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Chemical levels as of last night:

FC: 4
pH: 7.4
TA: 100
CYA: 60
CH: 240

The filter was backwashed July 3 in the a.m. pressues was 18 PSI. Next morning it was still 18 PSI. By Thursday a.m. it was 18 PSI. Late Thursday afternoon it had spiked to 28 PSI. The water is clear. Any thoughts on what causes the pressure to jump after a few days?
 
Shocked it on Monday and added CYA on Tuesday. Also added 80 pounds of salt. FC reading was 5+ for three days. Now 4. Before that we had trouble keeping the FC level up. It would fluctuate from 5 down to 1 over the course of a week.
 
The times don't match up quite like they should but close enough to hazard a pretty accurate guess at what's happening....

The filter is doing exactly as it is supposed to do...catching debris (in this case dead algae) and filtering it out of your pool water.

Your fluctuating FC, your ability to hold FC with a SWG, all point to algae growing in your pool (even though you may or may not see it) and then being killed by a big dose of chlorine.

If you haven't already done so, you need to backwash again.

read "The ABC's of Pool Water Chemistry" up in Pool School

If you can only test to 5ppm FC, you also need a much better test kit (FAS/DPD) to manage that big pool (and big investment)
 
mbowers104 said:
Shocked it on Monday and added CYA on Tuesday. Also added 80 pounds of salt. FC reading was 5+ for three days. Now 4. Before that we had trouble keeping the FC level up. It would fluctuate from 5 down to 1 over the course of a week.
Click to expand...

By the way you are using the term "shocked" you are probably not actually shocking your pool. Shocking involves determining the correct shock level of FC (usually above 10ppm) and holding it there until

1) the water is clear
2) you lose less than 1ppm of FC overnight
3) your CC is less than .5

This pretty much always takes a few days. Adding a chemical called shock is not the same as shocking the pool.
 
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