How often to backwash filter & other maintenance questions

sb127

LifeTime Supporter
Jul 16, 2010
32
Dallas, TX
I was just curious if most people go by the pressure gauge or by time. The PB said to backwash every month or if the pressure rises 10psi. Well, after 2 months the pressure hasn't risen 1psi. I've backwashed twice anyway, but just wondering if that is truly necessary.

Also, what about cleaning filter grids. Does that really need to be done twice a year like the PB said? It seems that if the pressure is staying in line, then what's the point of cleaning the grids? I like that sort of stuff, so no big deal either way....just curious more than anything. I don't see a reason to do more maintenance than necessary either.
 

arvil

Well-known member
Mar 7, 2010
52
Quakertown, PA
I have a cartridge filter so don't know much about sand or DE and backwashing, but, more than using the pressure gauge to see when I need to flush my filter, I see how much thrust is at the eyeball return. With a newly cleaned filter, I can hardly shut off the flow with my thumb. When I can shut if off fairly easily it's time to clean. I only have one return, so if you have more than one, it'll be different, but, you get the idea, just see what the return pressure fells like over time.
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
Unless something is going wrong, there is no need to clean the filter unless the PSI goes up. The only real risk to this approach is that the PSI gauges break sometimes.

On breaking down and cleaning the grids, it varies with the size of the filter relative to the size of the pool and how closely you get the recharge amount of DE right. I would start with what they recommend, but if there isn't any excess DE accumulating in the filter you can do it less often. You do want to break down and clean the filter when closing for the winter, so once a year is the minimum.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
22,069
San Dimas, CA (LA County)
It all depends on how much crud you are filtering out, really. My gauge climbs about 1 psi/month. At that rate, a teardown and cleaning annually is about right for me. I catch most of the visible stuff in a nylon stocking stretched over my skimmer basket, which I think helps a lot.

While it isn't that big a deal to break things down, I'd avoid it if possible. I work as a mechanic, and I'll tell you: it's pretty hard to break or strip something if you never touch it.
 

sb127

LifeTime Supporter
Jul 16, 2010
32
Dallas, TX
Thanks for the advice guys. It sort of went against my natural logic to backwash if the PSI hasn't gone up. I'm sure in the spring/fall the pressure will build much quicker due to all of the leaves and gunk that are going to accumulate in the pool.

JasonLion said:
On breaking down and cleaning the grids, it varies with the size of the filter relative to the size of the pool and how closely you get the recharge amount of DE right. I would start with what they recommend, but if there isn't any excess DE accumulating in the filter you can do it less often. You do want to break down and clean the filter when closing for the winter, so once a year is the minimum.
Our filter is 60 sq ft. For a 20,000 gallon pool does that seem to be normal, oversized, or small?
 

waste

TFP Expert
LifeTime Supporter
Mar 29, 2007
4,160
Coastalish 'down easter'
I hate to have to tell you this but ... you just don't have much debris in the pool that needs to be filtered out :p :cheers:

The pressure gauge (unless broken, in which case - the force of the returns) will tell you when the filter is in serious need of cleaning.

If you want to backwash when the pressure has only risen 1 or 2 psi, go for it! However, if you do that, you'll have to add the full amount of DE, as you'll have removed ~ all the old DE. (contrary to my advice here, where I assume a 8 - 10 psi increase before backwashing :) )

Sounds like your pool and water are in good shape :goodjob:
 

sb127

LifeTime Supporter
Jul 16, 2010
32
Dallas, TX
waste said:
If you want to backwash when the pressure has only risen 1 or 2 psi, go for it! However, if you do that, you'll have to add the full amount of DE, as you'll have removed ~ all the old DE. (contrary to my advice here, where I assume a 8 - 10 psi increase before backwashing :) )
Can you explain how backwashing the filter when the pressure has only risen 1-2 psi will remove almost all of the DE vs only 80% of the DE when backwashing with an 8-10 psi increase?
 

donaldm823

LifeTime Supporter
May 21, 2007
148
Cape Coral, FL
'waste' is the first post I have seen that confirms my experience that recharging the full amount of DE might be necessay if you backflush before 8-10psi rise. I backflush my DE filter every month and the press is only 1-2 psi. I always recharge the recommended nameplate DE amount (6lbs for my 60ft3 filter), and I have never seen an accumaaltion of the material during the winter breakdown. I tried once to wait intil the DE pressure rose-but found that it does not filter as well for pollen and the like. DE is relatively cheap so I go with the pool builders rec which is monthly or 8-10psi rise.
 

mynewpool

Well-known member
Mar 17, 2010
1,082
Spring, TX
sb127 said:
waste said:
If you want to backwash when the pressure has only risen 1 or 2 psi, go for it! However, if you do that, you'll have to add the full amount of DE, as you'll have removed ~ all the old DE. (contrary to my advice here, where I assume a 8 - 10 psi increase before backwashing :) )
Can you explain how backwashing the filter when the pressure has only risen 1-2 psi will remove almost all of the DE vs only 80% of the DE when backwashing with an 8-10 psi increase?
This is my opinion and I am sure someoen will comfirm. If you do it when it has only risen 1-2 psi, there is more than likley not much that was caught. Therefore instead of filtering out waste you are filtering out more DE. If you wait until a 8-10 rise, there is a lot more stuff so when you backwash you are getting all the dirt and stuff and less DE.
 

lightingguy

LifeTime Supporter
Jun 17, 2010
513
Glendale, CA
Backwashing pushes water backwards through the grids - so the DE and sediment is dislodged and removed.

Ideally when you backwash you would be removing all the DE - but there is no way to measure it. I think the pearls of wisdom article is just a rule of thumb 80%.

I've found with my filter there's no way of telling how much DE actually gets removed - especially if there's a lot of silt in the bottom of the tank. I've pretty much given up on the idea of backwashing for now and just break the machine down 3 times a year (Pool gets really really dirty in winter.) Last time my wife backwashed/reloaded very little of the original DE was removed and we basically got 2 loads of DE in. Needless to say the filter PSI was unhappy.

If you breakdown the machine sometime without backwashing it you'll see how the DE sits all over the grids on the outside.
 

waste

TFP Expert
LifeTime Supporter
Mar 29, 2007
4,160
Coastalish 'down easter'
I think we're zeroing in on this :cool:

Here's my take: as the DE gets congested with debris it coagulates. When you backwash, the water (as always) seeks the path of least resistance. If the DE on the grids is fairly 'uncoagulated' it all washes off, equally. If you've got areas of coagulation, those areas won't wash off, because the areas of lower coagulation have already been cleared and the water has no reason to try to dislodge the stubborn stuff.

With more time, I probably could have expressed this more eloquently, but I hope y'all understand what I'm trying to express :-D
 

donaldm823

LifeTime Supporter
May 21, 2007
148
Cape Coral, FL
Jason:
I recommend we add 'waste' comments to the "Pool School" section of maintaining filters. Most Pool filter companines are recommending monthly backflush vice a pressure reading. As such, your 80% recharge rule in pool school may be worthy of revision if you backflush monthly. 'waste' expnanation makes alot of sense and explains why some of us have not experienced DE buildup when we breakdown the filter for our winter period.
 

waste

TFP Expert
LifeTime Supporter
Mar 29, 2007
4,160
Coastalish 'down easter'
Don, it was your experience with your filter that got me thinking about this :goodjob:

I wrote the article on DE filter care and used 80% as a ~ safe amount to re-add because it wouldn't cause major problems from either over or under recharging the filter :cool:

Thanks for getting me to think! :wink: :bowdown: