Short Cycling

[PoolDoc]

I have a DE filter which will work fine for an hour (after backwashing) and then the pressure will rise and flow will virually stop. I have cleaned the filter with a commercial product and soap and water, nothing seems to work. The local pool store tells me there is nothing to add to the water to correct the algae until I have proper filtration.

Your pool store is full of it! Live algae plugs DE filters.

I'll never forget a night spent at a Girl Scout camp about 20 yrs ago -- they were my very first commercial pool customer, and it was my very first season, and the first and LAST time I ever let a customer pool turn green during the pool season. I got the call about 9pm, and was there from about 10:30 till 5am. They had a huge open pit vacuum DE filter that was BELOW water level. Every time the filter plugged, the water would overflow into the drain pit. The camp ranger and I were cleaning the filter every 20 - 30 minutes, all night long!

Kill the algae, and then filter it out. If you can, put your filter on recirculate. If you can't, turn it off, and add bleach till you kill the algae. Don't use other forms of chlorine, since you don't want it just resting on the bottom. On that GS Camp pool, it took 75 ppm of chlorine to finally terminate that algae. You can't go that high with vinyl, though.

With a 20K pool, you probably need to think in terms of 15ppm doses, though. That's around 6 gallons of household bleach per dose. Dose in the evening, and repeat everytime you find levels below 3 ppm. It may take many repeated doses, depending on how much algae is actually in the pool. Test with an cheap OTO kit (turns yellow from chlorine); DPD (not DPD-FAS) can bleach out, and cause you to think you have no chlorine, when it's really very high.

You'll probably get better results with low pH (~7.2) than with high pH (> 7.6) . . . UNLESS you had high CYA when you closed the pool, and now have low CYA. (Test to find out!). In that case, you'll need to RAISE the pH to around 8.0 with borax before you began dosing with chlorine. You'll get very fast algae kill, in that case, but you'll have to continue adding chlorine long after the water is clear, to get rid of all the chemical residue from bio-degraded CYA.

Do NOT mix in other algaecides. Adding copper when the chlorine is that high, will only result in stains. Adding foamy algaecides will just use up lots more chlorine. Polyquat could help, but it will be expensive, and you'd need to limit chlorine levels to something below 10ppm. And, it really works better if you've got a working circulation system, which you don't have at present.

If worst comes to worse, there are other ways. But they have complications and side effects. So, try chlorine first.

Ben

PS: Remember to add chems all around the pool, if your circulation system's not working. Pre-dissolve any borax in hot water.

[donjoarm]

OK. It's been a week and I have put 14 gallons of bleach in my pool over that time. I have the filter on recirculate since it continues to block every 20 minutes or so. The water is stilll green but the chlorine level remains high. Do I stay this course? I am brushing regularly as well. Thanks for the input.

[duraleigh]

Don,

You will have little success unless you get a drops based test kit and can test your water several times during the day. With that very high CYA level of 100, you need to put enough Cl in there to bring it to 25ppm and KEEP IT THERE until your water clears. As long as your water is green, you're not keeping your CL high enough.

Dave S.

[donjoarm]

I am beginning to get confused. One person is telling me to boost chlorine to 15 and add more when I get to 3 ppm and now I am being told to raise it to 25 and keep it there. Which is correct? How high can I raise my chlorine in a vinyl pool?

I do have a drop test kit but the highest it reads is 3 ppm. Where can I get one which will read 25?

Thanks.
Don

[duraleigh]

Don,

with a CYA level of 100, you will need to be around 25ppm to get to shock level for your pool. It then starts down immediately. Keeping it way at 25ppm as often as you can will accelerate the time frame it takes to clean your pool. I think the 15ppm level was recommended without noticing your CYA level.

If your test only goes to 3ppm it doesn't sound like a drops-based test. Go to Walmart, Lowe's etc. Better yet, spend the bucks and get Ben's kit...it's all you'll ever need.

Dave S.

[donjoarm]

Don,

with a CYA level of 100, you will need to be around 25ppm to get to shock level for your pool. It then starts down immediately. Keeping it way at 25ppm as often as you can will accelerate the time frame it takes to clean your pool. I think the 15ppm level was recommended without noticing your CYA level.

If your test only goes to 3ppm it doesn't sound like a drops-based test. Go to Walmart, Lowe's etc. Better yet, spend the bucks and get Ben's kit...it's all you'll ever need.

Dave S.

Dave-

If by drops based kit you mean the kind in which you add drops of OTO solution and compare the color with the samples, that is what I am using. Lowe's carries these kits which max out at 3 ppm and the Walmart kits max out at 5 ppm.

Is there another type of drops based kit? How high will Ben's kit read?

I have owned a pool for 13 years and have never had this type of problem so it is really driving me crazy.

Don

[waterbear]

Dave-

If by drops based kit you mean the kind in which you add drops of OTO solution and compare the color with the samples, that is what I am using. Lowe's carries these kits which max out at 3 ppm and the Walmart kits max out at 5 ppm.

Is there another type of drops based kit? How high will Ben's kit read?

I have owned a pool for 13 years and have never had this type of problem so it is really driving me crazy.

Don

First (I appologize if you already know this but sometimes it's good to start with the basics, I also appoligize for this being somewhat lengthy) there are 3 types of chlorine that needs to be measured:
Free Chlorine (chlorine that is available to act as a sanitizer)
Combine chloine (chorine that has combined with organics in the water and is usually not an effecient sanitizer)
Total chlorine (the total of both FC and CC)

Both FC and TC can be directly measured with the proper tests. CC is found by subtracting the FC from the TC. Ideally your FC and TC measurements should be the same. If they are not it is time to shock.

There are acutally different drop based reagents to test for chlorine

OTO (turns yellow) only measures Total Chlorine. Some people say that if you read it in the first 15 seconds it will give you a free chlorine reading and then let it sit for 2 minutes you can get a total chlorine reading but, IMHO, the results just aren't accurate (Walmart test kit has this in their instructions). It is good for a quick check on your chlorine levels when you know there are no problems or in some situations like yours as PoolDoc indicated.

DPD (turns pink) can measure both Free chlorine and Total Chlorine. It is a much better test but it has drawbacks. the differences in color are sometimes difficult to detect (especially for men) and it can 'bleach out" (turn clear) at chlorine levels above about 10 ppm leading you to believe that you have NO chlorine in the pool when you really have a lot! This can be overcome to an extent by diluting the sample with distilled water and multipling the reading by the dilution factor but this reduces the accuracy and can be time consuming. (dilution can also be used with OTO in the same way andhas the same problems)

FAS-DPD (also pink) is a titration test (pink color will turn clear to give you the reading...endpoint is DISTINCT) that can accurately measure very high chlorine levels (both FC and TC) (up to 50 ppm I believe) with an accuracy up to .2 ppm Combined Chlorine. It takes a bit longer than the other 2 but the results are easier to determine and much more accurate at high clorine levels, which is important when you are dealing with the type of problem you are having.

The general consenus that I have seen on this board (and I agree with it) is that OTO is good for a quick check and that FAS-DPD is good for actually determining your FC and TC.

Ben's kit which is sold on the sister website www.poolsolutions.com has both OTO and FAS-DPD tests in it. Taylor K-2006 is an FAS-DPD test kit. Either one is good. Ben's is a 'better bang for the buck'!

Both Pooldoc and Duraleigh are saying the same thing and it is sound advice. With the type of chlorine demand that you have your chlorine levels will be constanly dropping. You can put the bleach in your pool and then test it later and the level will be down! Algae creates a huge chlorine demand! You need to keep the level up and keep getting it back up.

Pooldoc's post is certainly is worth following since he is our forum moderator and has the experience to back up what he is saying. Dump in at least the amount of bleach he says and keep testing the water with OTO (since you will certainly have combined chlorine and you are really only interested in the total chlorine at this point) and EVERY TIME it drops below 3 ppm add more bleach. This could be several times a day. His note on pH and whether the pool opened with no CYA or high CYA is important. You never stated if the CYA levels are because you just added stabilizer or if they are from before. (the reasons are VERY technical but if you do what he suggests it will certainly be helpful!)

Once the pool clears and your filter is working might then be the time to start testing for CC and to keep the bleach levels up until it is 0 ppm.
As Dave (duraleigh) stated in his post, with a current CYA of 100 ppm you might need to go up to about 25 ppm FC to achive this. This is based on Ben's (PoolDoc) Best guess CYA chart. Here is that thread:
http://www.poolforum.com/pf2/showthread.php?t=365

[expose]

You'll probably get better results with low pH (~7.2) than with high pH (> 7.6) . . . UNLESS you had high CYA when you closed the pool, and now have low CYA. (Test to find out!). In that case, you'll need to RAISE the pH to around 8.0 with borax before you began dosing with chlorine. You'll get very fast algae kill, in that case, but you'll have to continue adding chlorine long after the water is clear, to get rid of all the chemical residue from bio-degraded CYA.

1)What do you do if you don't know what the CYA levels were when the pool was closed?
2}What would be the effects of having "all the chemical residue from bio-degraded CYA?"
3)How much chlorine would you add, and for how long after the water is clear?

[waterbear]

1)What do you do if you don't know what the CYA levels were when the pool was closed?
Don't worry about it and get your CYA level correct. (See second answer for what will happen if your CYA was biodegaded.)
2}What would be the effects of having "all the chemical residue from bio-degraded CYA?"
You would have a lot of ammonia compounds and urea in the water and your chlorine levels won't hold. You will also have a lot of combined chlorine.
3)How much chlorine would you add, and for how long after the water is clear?
You would add enough chlorine to bring it to shock level for the amount of CYA CURRENTLY in your pool (see this thread http://www.poolforum.com/pf2/showthread.php?t=365 )
and KEEP IT THERE until the Combine Chlorine is 0 ppm and your FC is holding. This might take a while and a LOT of chlorine!

Hope this helps.

[edarling]

Back to my original problem of clogged DE filter. I finally went out to undo the 15 bolts in my DE filter, and hose down the fingers. The DE was sooooo gummed up - it was like putty. I don't know what got into the filter to make it that clogged up, but it took a hose spayer on full force to get it out. I only added shock (for conveinience factor), bleach, and ph+. The algae was still active when I started the filter, so maybe I should have really shocked before using the filter to filter out the dead stuff.

Now I can re-add DE the normal way by draining to waste periodically, and the pressure is back to my pool's normal. I can do the normal to clear up the pool - add bleach to shock levels, vacuum, retest, repeat. WHen the pool is clear, I'll open the filter up again and clean it again for the season.

It does filter much faster with the filter than with my Aquabot I can almost see the bottom of the deep end. We've gotten so much rain this week (about 7 inches here, but lots more in other parts of NE) it has been hard to get the pool work in.

-betty