DE and algae flowing back into pool -- help me diagnose.

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impeller

impeller

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LifeTime Supporter
Apr 8, 2009
39
south of Atlanta
15,000 gallon in ground vinyl pool
Hayward Superpump 1 hp.
Pentair FNS DE filter
Multivalve
Pentair chlorine feeder
1 1/2 inch pipe

When the pump starts, I get a green/white jet out of each return for 10 seconds, and over time I get a little pile of sediment on the pool floor five feet from the returns. And it doesn't really filter very well...takes a long time to clean the water of algae. So something is wrong.

It has worked well in the past, but I have not been very good about covering the equipment in sub-freezing temperatures lately...maybe something has cracked. I just replaced all the grids and the manifold, and the big star-shaped gasket in the multivalve. No difference.

Then I re-installed the grids and manifold twice just to make sure I did it right. It is perfect. There doesn't seem to be anymore parts in the filter or anything else I can do with it.

Can anyone tell me what I should check at this point? I'm out of ideas. Thanks.



(I am planning to move all the equipment to a new location in a few months, so it will be very helpful to find out what equipment can be saved)

(I didn't install the system, so I'm not even sure it's hooked up right. Basically it goes from the pool to the pump--multivalve--filter--multivalve--feeder--back to the pool. No check valves anywhere...?)
 
The spring tension still feels pretty good, although not as strong as when new. When I turn it, it squeaks (or creaks) a lot...really loud, you can hear it a hundred feet away. When I replaced the gasket I honestly don't remember if I glued it down, or if I lubed it either. I have seen lots of discussion on this topic when searching the forum.

I'm happy to take it apart or whatever you recommend.


The multivalve is about 5 years old. It came with the filter.
 
And it doesn't really filter very well...takes a long time to clean the water of algae. So something is wrong.
Click to expand...

impellor,

Welcome to the forum. For clarity, filters do not filter algae out of your pool. If you have live algae it will continue to flourish in your pool until you kill it with something.......chlorine 98% of the time.

Then, the filter will remove the dead algae "carcasses" from your pool.

If you haven't found it yet, "Pool School" has some great articles on basic pool care.
 
Thanks. Great forum...I'm doing a lot of reading.

I wasn't aware that live algae could make it thru the filter. Apparently, the dead algae then (bright green stuff that comes out when I backwash) is somehow making it back into the pool along with some DE (and tiny bits of dirt), causing it to be cloudy and settle on the bottom.

The algae formed a few weeks ago when the plastic impeller threads stripped on my pump, and there were some days with no flow while waiting for parts, and also my being a bit late on this years startup. I think the pool chemistry is fairly close now, so I'm trying to narrow down this filter or valve problem.
 
There are really two unrelated problems here. DE should not be getting through the filter, and algae that is still green probably isn't dead.

It seems very likely that something is wrong with the filter. Normally I would suspect a torn grid. However, a torn grid is very unlikely with brand new grids. Still it is worth examining each grid. Another possibility is that the grids were somehow installed in the wrong order or the wrong positions. I am not familiar enough with that specific model to tell you what to look for, but with many DE filters some of the grids are slightly different than others and must be installed in specific positions Everything needs to be fully seated down and fit together just so to get a good seal. Also look for cracks in the manifold and stand pipe, and anything else you can see while the filter is open.

There is one other way for DE to get into the pool. A major failure of the multi-port valve could run water backwards through the filter in some situations. This seems extremely unlikely, since such failures normally have several other very obvious symptoms. To help totally rule this out, you might want to double check that no water is leaking out of the waste pipe when the multi-port is in the filter position. Practically every way a multi-port valve can fail causes water to leak from the waste pipe when it shouldn't.
 
If the valve is that squeaky you may have just knocked the gasket out of track again. Open it up and inspect. If it has come out again, replace the spring, shaft o-rings, and washers (or non-metallic bearings), and you may have to replace the spider gasket again.
 
UPDATE

OK, here's the latest. The pool is not green, only the DE mixed with algae in the filter, which is waiting to be backwashed. The chlorine level is fine since I raised it last week in order to kill algae.

So back to the valve/filter issue...

The pump has been off for 12 hours. I took off the top of the multivalve. All of the chambers have green water in them. Two of them, the input and the output to the filter, are full. So either:

A: When I took the top off, the green water flowed into all the chambers...so there's no way to tell where it came from.

B: The multivalve gasket is shot (although it looks fine) and the green water is going everywhere, including back into the pool.

C: The filter is not doing it's job and green stuff is coming out the output and back into the pool, especially at startup.


I guess it's good that I have not backwashed just yet, because this green stuff is our only indicator. As I said, the pool is relatively free of algae since my raising the chlorine level last week has killed most of it, but it is not crystal clear because particulates are still being pumped in.

My best guess is that I have a filter problem, and the green water in all chambers of the multivalve today was caused when I pulled the top off and water ran from the filter output chamber to all the others. This is the second set of "good" grids and manifolds and I'm quite sure they're correct. The only thing left is maybe a cracked standpipe due to freezing, which flexes open when under pressure, and hides at other times??
 
Welcome to TFP!!

While it's possible to have a hairline crack behaving as you suspect, it would be noticeable on close inspection.

Where the grids go into the new manifold, does the fabric go all the way up to the insertion point? Also, how is the o-ring on the standpipe (it shouldn't be pinched or missing!)? What about the air relief tube, is the fabric good and well secured? These are places that DE filters can also bypass and if everything else is good (ie. the grids and spider gasket/ multiport), would be the first places/ things I would look for. :-D

Please keep us updated as to how things go :)
 

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Thanks for the welcome. I appreciate all the help I'm getting here.

Starting to look like it's the filter, even though I 've been thru it so many times. As a former Marine Engineer and Diesel Mechanic, I think I've got the basic skills to make this work...just no pool knowledge.

Those are good questions you pose. I guess I'll have to pull that thing apart one more time and report back.
 
Hello,
I seem to have a similar problem where DE is getting back into the pool. I have pulled the filter apart and carefully checked the grids, but no tear were found. Were you able to determine the cause of the DE getting back into your pool?
Thanks.
 
Hi,

Welcome to the forum.

I was getting ready to give an update...just recently took out the old multivalve and installed a slide valve, and I completely disassembled the filter and inspected it. The filter was perfect. I believe the whole system is working fine now, but give me a few days to be sure.

The pool is a light green color now, so I can't be sure about the DE yet---long story short here...ordered the new valve from poolcenter.com (whom I've had good luck with in the past)...total nightmare!! Took two weeks to get it, never returned any of the 4 phone calls or one email. Told me it had shipped right away when it never had. Total runaround. Never again. Must be new owner or something. I'll be researching here for more worthy vendors.

Anyway, I'll give you an update in a few days when the pool is clear and I can be sure that the problem was indeed the multivalve. (Yes, I know most of you love the multi valve...but I had nothing but trouble with it, and never used half of all those silly stops anyway.)

I will be adding a three way valve somewhere after the pump to allow me to lower the pool level after heavy rains.
 
Here's my latest update on this DE problem...

I am getting much better results with the new valve. But, I still get a significant amount of DE into the pool on startup.

The Pentair manual says that you will get a little. I think the whole problem is caused by poorly designed and built pool equipment for residential use. Pentair generally ranks high on this forum and with my local pool suppliers, but I think their stuff is Crud.

So I'll be researching here to determine if it's worth going commercial. I would hope that, for instance, for three times the cost you can get ten times the quality (like Yugo to Mercedes Benz). We'll see.
 
are you dumping the powder into the filter basket, or are you diluding? The first two times I backwashed, I just poured the powder in and found de in the pool....or at least my tigershark did...lol...the last two, I put it in water first, then poured it in. I didn't have that problem again.

Just a thought from a noob...
 
After observing my setup for quite awhile, my non-expert guess is that after pump shutoff, the water in the filter slowly drains back thru the pump and into the pool. When this happens, some of the DE falls off the grids. Then when you start it back up some of the DE flows thru those "holes" and enters the pool. After a few seconds the "holes" are once again plugged up by the DE layer.

Makes sense to me anyway.

On my new setup I intend to put a check valve before the pump to see if I can prevent that drainback thru the pump after shutdown.
 
Impeller,

the water in the filter slowly drains back thru the pump and into the pool.
Click to expand...
If that's the case, you can stop that flow by finding the leak that's letting in air.

If the system is airtight, the water will stay in the filter. If it's draining out of the filter, the draining water has to be replaced with air (most always coming from a suction-side air leak).

Find that leak and the issue will stop.

Now, please do not take this the wrong way, I am not intending to be rude, but it does not appear from your posts that you have a good grasp of the function of chlorine in your pool. Any indication of green in your pool implies the need to elevate your chlorine level and kill the algae. You can never filter green algae from your pool.......chlorine has to kill it.

It does not appear you are understanding the importance of chlorine and the fact that it is constantly consumed in your pool and must be constantly replenished. Pool School has some very good articles. I would suggest "ABC's of Pool Water Chemistry" as a start.
 

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