With some help from the board, I'm coming to the conclusion that my sand filter might be too small for our pool. I only get about 15 minutes of decent pressure when vacuuming and I can vacuum one day and have a bunch of dirt deposited the next day. As best I can estimate, our pool is around 11,000 gallons. The normal pressure on the filter is 10-12psi, but then it shoots to 20psi after about 15 minutes of vacuuming and I lose all suction.

The current sand filter is a Pentair 40D which houses 175lbs of sand. It's 2-3 years old, but was a home warranty replacement, so we didn't have any say (or knowledge) when it was replaced. It's being run by a 3/4 HP pump motor and the filter/pump are 29 feet from the pool. One skimmer and 3 return jets.

If this filter is indeed too small for our pool, I'm considering a new one. Any recommendations on the proper size sand filter? Any recommendations on sand vs. DE vs. Cartridge?

Thanks for your input.

If you were happy with the clarity your current sand filter provides, then get another one. They are generally the easiest to manage.

As for size, get the biggest you can afford/your equipment area can handle.

Two things come to mind...

1. The filter is too small. rated at 40gpm, you pump is producing much more volum than that. I would suggest the TA100D (100gpm) as a really good (much bigger) match for your pump.

2. Frequently, the excess dirt you find in the bottom of your pool is actually dead algae. YOu may not have adequate chlorine in your pool. If you are confident that is not the case (you can't always see algae) then it sounds like a larger filter might be a big help to your system.

How would I know if the deposits I'm seeing are dead algae or dirt? If it's dead algae, why does it keep reappearing? They are large, streaky clumps on the bottom usually. Not a fine, powdery even coating that I would associate with dirt. I guess the question is, how does more chlorine 'remove' the dead algae?

Thanks!

What color are the "large streaky clumps" and what additives have you used in your pool besides the basics used with the BBB method. How about water appearance, color, clarity, smell, etc.? Current pool testing numbers? How long has this been occurring. Are you just opening the pool from a "swampy" condition? What does the stuff feel like. Slimy?

Large stringy clumps reminds me of the biofilm a body of water can develop that is usually a resistant bacteria that sets up in water, filter, pipes, and other equipment.

gg=alice

Both dead algae and very fine silt can be suspended in the water and then slowly deposit onto the floor over a period of days in a pattern that depends on how good the circulation is and where any small imperfections in the floor are.

The almost enough chlorine but not quite enough leads to dead algae things works like this: If there is any algae at all, it is constantly growing. If the chlorine level isn't high enough to kill all of the algae, it will still kill some of the algae. Normally, this will happen fairly quickly, and you end up with either no algae at all, or no chlorine at all. But if the CYA level is relatively high (say 60+) you can get into a situation where CYA is releasing chlorine that it has bound up to replace the chlorine that is getting lost killing algae. The active chlorine level remains too low, so it never kills all the algae, but the CYA has so much chlorine bound up in reserve that you don't run out of chlorine either. The net effect is that there is some algae, but only a little, actually alive at any given point and dead algae is constantly raining down on the bottom of the pool. Raising the FC level a little can bring the active chlorine level high enough that you finally kill all of the algae and dead algae stops raining down.

Chappy,

Posting a set of test results will really tell us a lot about the condition of your pool water and whether algae is a suspect.

How does your water look to you? Is it crystal clear?

All very interesting. My water currently is very clear - I didn't let it get green and swampy this spring. I've been putting in a few gallons of bleach every week for the last 2 months, just trying to stay ahead of the game this year and avoid any sudden spring "swamp-ups." I adjusted my PH last weekend, it's right at 7.4, and I also checked the CYA - if it's possible to be at 0, that's sure what it seemed like. I can get a full set of results tomorrow though. I have only been running the pump for 3-4 hours a day lately, so the circulation is not great. Again, we're not swimming yet, but I just want to stay ahead of the game.

Now I understand the scenario where there is just not enough chlorine to kill all the algae, so it's constantly raining down to the bottom - that makes sense. Maybe I'll try a big dose of chlorine and see if the deposits don't disappear for good.

I'm not having any major problems here, just trying to understand better 1) the limitations of my current filter equipment and 2) why when I vacuum the bottom doesn't seem to stay that clean for very long. You guys have already helped me understand both points much better. This forum is the best.

Just make sure you up your CYA a little and on the "big" dose - don't over shoot your shock target.
On the CYA test - is it completely clear or is it a little cloudish looking? You might have somewhere between 0-20 and its just not enough to register on the test vial...

If the dust/dirt/pollen/dead algae dissappears when the pool is at shock level and stays away for several days, it was probably algae. If it's still there even at shock levels then it's prob dust/dirt/pollen. Sometimes Mustard Algae goes away at shock levels and then reappears when the FC drops down to "normal" levels.

What should my target CYA be? When I did the test, it stayed clear the entire time. What do I use to raise the CYA - I've never had to do that before. Do I need to wait a specific amount of time after raising it before I do the "big" chlorine dump?

And at shock levels, if it is dead algae at the bottom of the pool, will it just disappear? Or should I vacuum it up first and then see if anything reappears?

Thanks for the help.

With no CYA and adding chlorine only every week, you probably have several days of zero chlorine per week. To raise CYA, you need to buy stabilizer at walmart, HD, Lowes, pool store, etc. It should say "cyanuric acid 100%" on it. Dead algae won't disappear with chlorine, it needs to be filtered out.

Your filter is too small, but having algae get started then get killed on a weekly basis is the bigger issue here.

Sometimes it says 90%, 94% so if thats all you can find its okay to use.

Vacume it up - if it reappears while the pool is at shock level - it's not algae.
Target 50 ppm for your CYA. Use "the sock method" for adding it - put about 2 lbs at a time in an old sock, tie a knot, and use string to tie the sock off in front of the return where it will dissolve. Retest the level in 5-7 days, and adjust your FC levels according to the CYA chart - as it rises, so will your FC requirements.
No. Add the CYA, the first day your shock level is 10, and as the CYA dissolves its safe to assume the level is increasing so the next day your shock level is 12, etc. next day 16 and by the time the CYA has dissolved out of the sock your FC shock level is 20. You hold it at shock level until the FC holds over night and your CC is .5 or less. I doubt you'll see any algae if you follow this process. At first you'll see dead algae on the bottom but once you vacume it out it shouldn't return. If you do see a residue on the bottom and your FC is holding at shock level, then that's just dust/pollen.

What comes to my mind is that you are not running the pump/filter for a long enough time period. My pool is 11,000 gallons. My pump is 1 1/2 hp (too big, I think) and the filter is 18" using 150 lbs of sand. I run it for at the very least 8 hours per day. During start-up for the first 3 or 4 days it runs 24 hours until water chemical make-up is good, including hardness and metals.

Curious, I Have a similar setup, what makes you think pump is to big? Mine was a package from a reputable dealer, I run about 8 hours per day (4 afternoon and 4 eveing). Water is clear for most part, when I have light on I notice little looks like white squares suspended in water when light on. Think it is byproduct of shock or water is not polished whatever that means. My media is pea pebbles with zeo on top, again dealer sert me up with that or sand, been happy so far.

Mainly because the forcefullness of the returning water. Our original pump was not this forcefull. It literally throws you across the pool! LOL When I try to vacuum, it loses all suction almost immediately due to collapsing hose going from the skimmer. Tomorrow we will be hard piping that last hose to see if problem corrects. We've had the pool about 8 years now and never had a problem until the last year or so. Always been a headache to vacuum.