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Common Mistakes in Backwashing DE Filters

dirty DE filter in need of replacement and cleaning


The most common mistakes people make when backwashing a DE filter.

There are some common (and not so common) mistakes that people make when trying to backwash their DE filter. If you are having problems with your DE filter, the problem might not be your equipment. The problem might be you. (yeah, the truth hurts sometimes).

Here are the most common mistakes people make when backwashing their DE filters

Not adding enough DE

Let me ask you a question. How much DE can you get into a one-pound coffee can?

If you answered “one pound” then please take a moment and kick yourself. A one-pound coffee can will hold approximately ONE HALF pound of DE. So, if you’re adding 5 one-pound coffee cans full of DE to your skimmer after backwashing, then you’re the reason for the poor performance of your pool filter.

If you do not add enough DE to your filter, then the grids are not totally coated with DE. The dirt that goes into your filter will attach itself right to the fabric on the grids and will not backwash off. This will cause your filter to short cycle (go very short times between backwashing).

Only backwashing one cycle

OK, lets see a raise of hands here… how many of you only run one backwash cycle (put it in backwash, then put it back into filter) before you add DE back to the filter and go back into the house for another beer?

If you raised your hand, then as you are putting your hand back down, slap yourself in the back of the head. Repeat after me “every time I run a backwash cycle, not all the DE and dirt comes out of my filter.”

By reversing the direction of the water through the filter several times, you’ll do a much better job of flushing out the DE and dirt that’s trapped between the grids. You will never get it all out, which is why you need to do a complete filter clean every six months.

Running a short “bump” to bring your filter pressure down

I shouldn’t even be telling you this, but here goes… if your filter pressure is high and you put it on backwash for, lets say 5-10 seconds, you can get pressure to come down. Like most any shortcut, it is a really bad idea.

It reminds me of a story my mother told me about when she was in college in the 1950’s. They were all making dresses, some of the girls ran short on time so they glued and ironed the seams instead of sewing them. Let’s just say that their shortcuts weren’t the only things that were exposed.

But I digress. Running a short bump will make a difference for about 5 minutes at the most, then your filter pressure will go back up. If you don’t catch it in time, the high pressure will ruin your grids or manifold.

Not adding DE right after backwashing

We have all been there, right? You backwash the filter, look in the shed and all you have is an empty DE bag, or perhaps a bag with only a handful of DE in it. So, you leave the filter running for a few days without DE until you can go to Pool Stop to chat with Paul and the guys and get some more DE.

Here’s the problem. While you’re inside watching the game, all the dirt in your pool is coating your filter grids and it will not backwash off. Don’t be surprised if your filter starts to “short cycle”. So here is the deal: Suck it up, record the game and make that trek to the pool store for some DE, or else turn the filter off until you can go get some DE powder.

Not emptying the skimmers or pump trap before backwashing

If you ever clean a DE filter, you might see a bunch of leafy material stuck inside the filter grids, and you shake your head and say “how could that ever get there?”

Here is how it gets there. When your filter pressure increases, your overall flow goes down. When you put the pool into backwash mode, all of the sudden. VOILA. the flow suddenly increases and a bunch of that stuff that was sitting lazily in the skimmer or pump basket is suddenly flushed out and where does it go? Well, since you are in “backwash” mode, the water enters the inside of the filter grids and all that crap goes with it. So kids, the moral of the story is this: Always empty your baskets before backwashing.

Adding DE while the filter is still in “backwash” mode

Before you add DE to your skimmer to recharge the filter, double check to make sure that the pool filter is back in “filter” mode, and not in “backwash” mode. This is one of those things that you realize just a little too late, and by the time you realize it, there is nothing you can do about it.

If you add the DE while you are in “backwash” mode, then all that DE will go into the inside of your grids and you’re stuck with no good options. Either you can go ahead and put the filter back into “filter” mode and watch all that DE pour back into your nice clean swimming pool…OR You can tear apart your DE filter and wash down all the grids manually to get that DE out. IF you’re lucky enough to have a multiport backwash valve, then you could put it in “rinse” mode to just blow that DE out to the sanitary sewer. Most people don’t have this type of valve.