Why Does My DE Filter Lose Pressure

[AnnaE]

We opened our pool this year and everything was going fine. We cleaned the DE filter, put in the DE and the pressure was fine. However, after 1.5 hours, the pressure was gone. We primed the filter and then the pressure is good again. But then, it loses pressure again. Can anyone tell me what is going on? We've had our pool and filter going on 8 years. This has never happened before. We did backwash because we had a lot of algae. We put in more DE and at first, its fine, then no pressure. How often does these filters need to be replaced? Is it time for a new one? We got a new pump two years ago.

Many thanks.

[PoolDoc]

I'm guessing the problem is with losing prime, not with the filter. The filter is just where the gauge happens to be.

Check at a return, and compare flow when the pressure is high, with what it is when it "loses pressure". Low flow with low pressure USUALLY means low pump output.

A very common cause of prime-loss is a suction leak, often at the pump strainer lid gasket. If you want to send pictures of your pump, filter & piping, we might be able to spot some other places to look.

[gkrupkin]

I have same problem. DE filter pressure jumps from 20 to over 30 in like 1 hour after backwash and pump loses its prime . Pool is still dirty so that could be an issue. But when i put on recirculate I dont have any problems. I was thinking maybe my DE filter needs to be opened up and cleaned out...

[AnnaE]

Sorry I never replied back in 2012 (LOL)!. We did eventually figure out what the problem was. As I stated, we had a lot of algae. We had to backwash a few more times and add more DE before the pressure stabilized. Since that time, we haven't had another problem. We just know that when we open the pool, we have to backwash at least three to four times due to the algae built up.

[gkrupkin]

So after pulling apart my filter and cleaning it yesterday, it worked great for about 3 hours and then psi jumped to 30 from initial 20 again. What concerns me is that when it goes up like that I start noticing little air pockets in pump basket. They were not there before nor do they appear when I have it on just recirculate. I've been reading the stickies on if leaks. Am I going crazy or do I have a leak problem somewhere ? But why forest it take a few hours to show up?

[SunnyOptimism]

I have a Pentair QuadDE-100 filter and it works beautifully. I tear down and clean out my filter at the end of every swim season and my pool runs all year round.

Can you describe what you did to clean it and how you did your re-charge of the DE?

If you had a leak on the pressure side of your system, your pressure would not go up, it would go down. For your pressure to jump 10PSI like that means the filter is either picking up "stuff" (which it's supposed to do) or there's some issue with the internals of the filter.

My QuadDE uses cartridges to hold the DE unlike your FNS Plus which uses the older style DE grids. Both are susceptible to tears which can cause funny pressure problems. The top and bottom manifolds that hold the grids need to be carefully inspected for cracks and broken gaskets as they can cause a by-pass of water which would be seen as a low pressure and then, when they plug up, the pressure will rise. Also, there is an air-bleed on the top assembly that allows for air-relief (as well as the high-flow bypass air-relief valve on the top of the unit which you can do a quarter turn to open). That inner air relief can sometimes cause problems.

I'm just spit-balling lots of things that can go wrong inside a DE filter (now you know why so many people prefer the simplicity of a sand filter ).

[gkrupkin]

Thank you for the response. I cleaned it last night. Took the filter apart and pulled out the whole thing and using a hose cleaned off all the wet DE. I must have cleaned it for an hour. I then put it back together and turned everything back on in the "Filter' setting. Then I used 12 cups of DE into a 5 gallon bucket and mixed it with pool water then poured it into the skimmer. Pressure remained around 20PSI for about 3-4 hours then jumped to 30. Normally I would think that its just a dirty pool and this is normal. Pool is getting cleaner but is still cloudy and not completely clean. Reason I'm concerned is I suspect I see some air bubbles in the pump and when the pressure jumps to 30 it starts to lose its prime. The water level seems to be a bit lower in the pump. But based on your last comment, it sounds like if it was an air leak problem the pressure would be dropping not rising. So maybe I've just got a dirty pool and it is what it is.

[SunnyOptimism]

Ok. You've got a lot of symptoms that I need to ponder but I can't address them now as I am mobile the Pool Forum software sucks on mobile devices. One thing about bubbles in the pump basket is they are typically indicative of a suction-side leak, usually the o-ring that seals the pump basket cover. Check that to make sure the seal is still good. I also have some issues with your filter startup procedure that I'd like to detail in another reply when I get back home. You're doing it ok, but I think there's some room for improvements there. I'll detail what I do and you can spit-ball it to see if you it'll work for you.

Talk to you soon.

[SunnyOptimism]

Sorry, I wanted to reply sooner but yesterday fell apart on me so I just couldn't get to it.

First off, properly cleaning a DE filter takes a lot of time. It takes me a good 4 hours to clean mine so I know how you feel.

OK, here's where I'll talk cleaning and recharge procedure. I realize our two DE filters are different internally but I think the process is the same. You mentioned adding 12 cups of DE to a bucket and then pouring that into the skimmer. So that brought up questions in my mind -

Are you truly adding 12 cups (as in a standard 8oz cup) of DE? Do you know what that is in weight as DE filters typically require a starter charge (full charge after cleaning out old DE) that is measured in pounds?

I use a orange plastic DE scoop that I got from the pool store. It is larger than a standard coffee can. It is designed to roughly hold enough DE to equal ~ 1/2 pound (DE has a very low weight to volume ratio). My QuadDE-100 requires a 10lbs starter charge and then 2-3 lbs per backwash. Here's my procedure for starting the filter after a full clean out -

1. Run the pump on high speed and set valves so that all of the suction is on the skimmer
2. Mix 1-2 scoops of DE into a 5 gal bucket of pool water and keep in suspension as best as you can

3. VERY SLOWLY (while keeping the DE stirred) add the DE to the skimmer. Try to take 30sec to 1 min to empty bucket

4. Repeat steps 2-3 until 10lbs (20 scoops) of DE is added.

5. Note filter pressure (my clean system pressure at low speed is typically 10-11PSI)

6. Leave filter running at high speed for a minimum of 1 hour. Set back to normal speed and run the pump for a minimum of 8-12 hours. DO NOT ALLOW THE PUMP TO SHUT OFF DURING THIS TIME.

7. Reset all pumps speeds and valves to standard operating positions and note clean filter pressure. If it's not at the typical pressure, add some extra DE as-needed.

So the reason why I follow this VERY SLOW start procedure is this - DE settles out of suspension in water fairly quickly. You can see it by mixing DE in your bucket and watching it. Within 30-60sec, the DE mostly settles on the bottom. The settling time is shorter the more DE you have in suspension. Therefore, if you load up a huge charge of DE into a small volume of water, it can very easily settle in your pipes rather than make it all the way to the filter. I use my pumps high speed to ensure that the DE gets sucked as rapidly as possible to the filter so that the turbulence ensure that the DE reaches the cartridges.

When you opened your DE filter, you must have noticed all the DE piled up like beach sand in the bottom of the filter. For the most part, a lot of your DE sits on the bottom of the filter an only a small fraction of it coats the grids (or cartridges in my filter). Thereofore, when you start up your filter you want to make sure the DE gets to the grids and stays there. That is also the reason for letting the pumps run for a long time afterwards. You want to make sure the DE embeds onto the grid material so it stays there.

The weird fact about DE filters is that they work better when the DE is a little "dirty" as opposed to fresh. The "dirt" and "gunk" helps keep the DE plastered onto the grids. Fresh DE charges have a tendency to slough off the grids when you turn the pumps off and thus uncovers the mesh. Then, when you start up, the DE gets mixed up with water and re-coats the grids. This is also the reason why on a fresh DE charge, you'll see what looks like dirty water coming out of your returns for 30secs or so after turning on the pump. That arises from the fact that there are areas of your grids that are not initially coated with DE and so the "dirty water" gets through. Once those areas clot up with DE, the filter starts working normally.

As for your sudden pressure rise, I have seen that too on my system. As I'm charging the DE into a cleaned filter, the pressure gauge barely budges. Then, on that last bucket of DE, the pressure rapidly spikes up. It could be that you have excess DE in your lines somewhere and, over time, the pressure spikes up as the grids become fully coated.

If you're experiencing a high system pressure and loss of prime in the pump, that could be a symptom of too much DE in the filter.

Let me know what you think.

[gkrupkin]

First, thank you for taking the time to help me. You are correct, I"m using a red 16oz cup. I've already ordered a DE Scoop cup last night. For now, is there an easy to way to figure out how much DE i need using my plastic cup?

Also, how do I run the pump on high speed? I know there are main drains and skimmer drains. I do have 2 pipes coming into my pump and 2 going back out. But they are not labeled. I assume I need to shut off the main drain and do only skimmer and that would run my pump on high speed? I'm trying to insert a pic but I can't figure out how.