Need help figuring out problem with DE filter

[westchester]

Have 72" Pentair DE filter. Replaced small grid which had holes. Cleaned all grids using dishwasher detergent. Reassembled and charged with 7 pounds of DE. Green pool. Pressure started at 15 but went to over 30 six hours later. Each time I backwashed and added small amount of DE the cycle time has decreased. 2 hours became 1 hour. Before backwashing when pressure was up to 35 I opened tank to look and see what shape filter was in and it had fairly thin algae film across all of grids but it wasn't really that built up. The metal "mushroom" on top of maninfold had 1/4" of stuff on it but the grids were more like a film. Just doesn't seem to be enough to explain the high pressure and the resulting slowdown of water flow. Pool is green but this short cycling is making it impossible to get any real water flow and I don't want to shock it until I'm in a position to really filter.

I've cleaned filter four times this summer (two times where I put it completely apart) and I'm thinking there is something else going on. Grids are around four years old and pool wasn't opened last two years. Wondering if grids have gone bad or if a full chemical clean would make a big difference. Any suggestions on what to do? I did notice that lines going into filter occassionally leak when I backwash.

 

[westchester]

To see what was going on with filter grids, I also tried a short backwash with tank top off; grids inflated like bladders with water going in tubes; is this normal? Made me think grids were clogged. This could explain leaking in pipe going into filter when I backwash. If water isn't easily getting out of grids, then it also isn't easily getting in and that could explain short cycle time, with just a little material clogging them up more. How can you tell if filter grids have gotten too sealed up?

 

[Bama Rambler]

You have algae and it will clog a DE filter very quickly. You should be shocking your pool. There's an article in Pool School on how to properly shock your pool.

You need to shock it now and the filtering will take care of itself. You haven't said anything that makes me think there's anything wrong with the filter. Everything you've said sounds perfectly normal for a DE filter when you have an algae outbreak.

When you backwash the filter you should add 80% of the new charge of DE back to the filter.

 

[westchester]

Backwashed this afternoon and pressure went back up over 30 pounds within 30 minutes; at that rate I'd go thru 100 pounds of DE per day. When I opened tank the filter was mostly green but it was a very very thin film; much thicker on "mushroom" on top of manifold which made me think that filter membrane wasn't as porous. Does dead algae not clog filter up as much?

 

[Bama Rambler]

Dead algae won't clog quite as fast, also once you start killing it, it won't be growing and multiplying so every backwash gains on it. Right now it's growing faster than you're getting rid of it so it's a never ending cycle.