New to DE filters...need some help

Ok, I have read the stickied thread on DE maintenance and done some other research, but it seems there is some conflicting information, so I just want to get the straight scoop on everything!

I've been in a home with an in ground pool for the last 3 months (renting), and it has a Pentair FNSP36 DE filter.

We had a pool guy coming and doing maintenance, and one time we had to pay him extra because he said there was stuff coming back into the pool (either DE or dirt) when the filter was running. He replaced three of the DE filters as they had holes in them.

We ended up having to fire the guy and are looking into doing the maintenance/upkeep ourselves or getting someone else down the road. All we ever saw him do was come in for 10-20 minutes, skim the top, throw 2 chlorine tabs in the floater, and vacuum very briefly. My wife and I went out there several times to comment on this and he said it was all the pool needed. Well, after he left, we would spend 30 minutes on vacuuming and the pool would look much better. Sorry, but that's not worth $130/month in my book. Especially when he charged us a bunch extra for the filter maintenance.

Enough of that though, here's where we are at. My parents owned a pool before so I'm familiar with the chemicals/testing side (though I want to switch to the BBB method as that is new to me), however it was a sand filter. Every time we were done vacuuming, we'd simply backwash it and then set it back to 'filter' and be done with it.

What I've been reading is with a DE filter, you need to backwash it only when it goes 8-12 psi above what it was when cleaned (for me after the pool guy came, the psi said about 18, so I'm guessing 26-28) OR once a month. Then when it's done backwashing, apparently you lose all the DE that was in there, so you have to fill it back up with DE based on the square footage of your filter (which for me should be 36).

Onto the questions:

1) I thought a filter was a filter and screwed up the first time. The PSI looked high to me at 20 psi, so I ran backwash on it 2 days ago but the water through the sight glass was pretty immediately clear...I'd say it backwashed for maybe a minute. I then turned it back to filter and went on my way. Did I just lose all that DE? Should I just backwash it for xx minutes to ensure all DE is gone and then add the correct amount for my filter? Do I now need to break down the whole filter, wash them all with a hose, and then put it back together again? Should I turn my filter off now until I can add the DE back in or do maintenance?

2) How often do I want to backwash? Is the 10 psi above standard OR once a month correct? I *never* saw the pool guy replace any DE in the three months we've been here, and I wasn't here when he actually serviced the filter itself.

3) I have about 18 pounds of Food grade DE laying around. Will this work the same as the pool-quality DE? I'd like to use it up...don't ask how I got 20 pounds of food grade DE...long story.

I live in Texas, so the pool is ran all year long. It's definitely not in the best condition...I know it could use a full drain and then redo the liner (which looks like the painted kind), as there are parts where bare concrete is showing just from constant wear. However, the house is a rental that was built in the 60's and the owner is trying to sell the house at some point, so I doubt he's interested in any big maintenance like that.

Please let me know if I need to provide any other info. Thanks so much in advance!

My DE filter runs around 12PSI when freshly back washed. I back wash when it gets to 20PSI and add 4 coffee cans of DE. Been using this system for years and pool is crystal clear. Don't get too hung up on the exact psi increase etc... I'm not sure of the difference between pool grade and food grade DE other than you can use food grade in your garden to control crawly thangs :)

Throw a couple cans in and forget about it until you see a pressure increase and then start from scratch .

Welcome to the Forum!

I wrote the "use and care for DE filters' and it was based on the pools I saw as a service tech and was meant to tell folks how to avoid the problems I had to go fix.

You most certainly have to replace DE after you backwash the filter!!! (it's in the stickie)

As for frequency, I'll stick to what I said, "when the PSI rises 8, it's time to backwash and then add ~80% of DE that you would, when the filter is new or manually cleaned" - however, if you want to backwash more frequently, you'd need to increase the % (of a fully clean filter) up from 80%.

I'm sorry that I don't know anything about 'food grade' DE, perhaps someone else does and will chime in.

I hope this post helps you a little, if you need more info - I'm here on weekends and there are a number of other folks that will help you :cool: