sand filter vs cartridge

I have a 25000 gallon inground pool with a vinyl liner and a hayward pro series plus sand filter.
We often have problems keeping the pool clear. Recently we had to shut off the filter for 24 hours after we added some kind of algae killer and a bunch off white residue had to be vacumed out of the pool. Now we seem to have some green dust on the liner that we can brush off but it seems to be floating in the water and the filter does not seem to clean it out. we just replaced the sand just in case there was a issue with parts broken in the filter and i could not see anything wrong when i replaced the sand. We use the 3" tablets in the skimmer basket and have a test kit i can post numbers tomorrow.

Hi and welcome to the Pool Forum. We will need some more information to be able to help. Post a complete set of current water testing results taken with a drops-based kit. Also, tell us ingredients of what you have added to the pool. (Not product names or just 'shock.') Then somebody here can try and help you.

Also, you should never have to replace the sand in a sand filter unless some additive has gummed it up. We moderators all use sand filters and none of us changes our sand. Mine is the "youngest", in its 9th season with no problems.
That doesn't mean we endorse sand filters over cartridge or DE filters.

All three can do a marvelously fine job if sized and set up correctly, and then maintained correctly. If you are having a problem with your filter, and your filter is undamaged, it's either due to another part of the system having a problem or the filter's too small for the pump, the pool, or both.

Carl

just wanted to let you know you now have general access to the forum. -ben

I checked a couple of things last night and here is what I got
PH 7.2
FC 12
CYA 50
We have two three inch pucks in the skimmer, and I added a couple of pounds of PH+ (not sure of exact brand, will repost) and 2 gallons of Namco liquid shock. I will check levels again tonight. I had to brush the sides again to keep the green (algae?) from accumilating. filter is running 24 x 7 right now.

OK. Take the pucks out. They are making the pH go down and the CYA go up. Unless you have a good reason to raise CYA over 50 its a good place to stop.

PH+ is overpriced, seriously overpriced Arm&Hammer Washing Soda (not baking soda), that sells here in NJ for .80/lb It's soda ash, aka, Sodium Carbonate. So is Washing Soda.

Namco Liquid Shock is merely 12.5% Liquid Chlorine...double strength bleach. I buy the stuff when it's on sale because it gives me 1 gallon jugs that I KNOW are safe for 12.5% I then refill them from 5 gallon carboys of 12.5% which is far cheaper. Two gallons should raise your FC level by 10ppm, which may bleach your liner a little, as 22ppm is higher than the 15ppm we recommend, but probably not, is my guess.

Carl

should I continue to keep the FC high for a couple of days?

Yes, when fighting an algae bloom, you need to keep your chlorine at shock level for your CYA until the pool clears, the algae is gone, and you are not losing more than 1 ppm of chlorine when testing at night after the sun is off the pool and again in the morning before the sun is on the pool. After you've met all three of those conditions, then you can let your chlorine drift back down into normal ranges for your CYA.

Janet

There is a trick of adding a little DE to a sand filter to get better filtration if you're looking to trap really small stuff.
Check this thread:
http://www.poolforum.com/pf2/showthr...to-sand-filter
The first post tells you the process. If you do this just keep a close eye on the pressure as it will rise quickly if you're catching stuff.
You then backwash and start again. If you really have a mess, like I have at times, I just do a quick backwash to dump most of the crud. I don't try to get the BW water totally clear until I've eliminated most of the crud. Saves water.
Al

Also note that when you add the DE, the pressure may not rise instantly. Mine takes about 20-30 minutes. So don't add more if you don't see the rise immediately. If after a half hour or so you don't see a 1 psi rise, then add a little more.