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Pool pumps, pool filters and the plumbing of
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Ray1031
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Postby Ray1031 » Sat 28 Mar, 2009 11:11

JPlunket wrote:In the meantime, I've used a 50/50 mix of water/acid, let soak 30 minutes. Solution turned green, without much bubbling. THere were bubbles, but nothing close to a foaming action.

Put the filter back, and have lower pressure than I've seen in a while (correction of the psi's cited above: I've been no lower than about 17psi for months, and it has typically risen quickly to 27psi). Pressure after hosing off, then thorough cleaning with Cascade in hot water, then a 30 minute soak in acid solution is about 13psi, down from 25psi.

Any thoughts?



Believe me, if there were a calcium buildup on your filter, you would have seen foaming and the color change would have been more towards the yellow, than towards green. To me, green tinting during an acid wash usually indicates the presence of live algae ... common algaes, not mustard/yellow algae. When you treated for the mustard infection did you also shock the pool and add a common algaecide? Quite often, as the mustard/yellow algae plays hell with your chlorine levels, it will allow the more common algae green and black varieties a "toehold" in the pool. These algaes are often somewhat protected from chlorine treatments by a greasy coating on their hides. Common algaecides are pretty much 70 to 80 percent soap and cleans away this greeasy coating so the chlorine can more readily attack the algae itself.

Ray


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JPlunket
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Postby JPlunket » Sat 28 Mar, 2009 11:44

Ray,

Thanks again for the specifics. I actually followed most of your advice, based on what you said earlier in this post and a couple others. As noted the effect has certainly been salutary.

What do you make of the minimal bubbling and green coloration of the acid mix after the 30 minutes soak?

Is it the case that calcium builds up in the filter pores when CH is high (mine's 500). Does the acid soak clear the calcium out completely in such a short soak (30min)?
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Postby JPlunket » Sat 28 Mar, 2009 13:44

Sorry to be obsessive, but what would be causing my filter to clog so quickly?

conditions:
water temp 83
pH 7.2
TA 150+
CH 500+ (plain tap water is 200+)
CYA - ran the test, black spot disappears at 1.5-2ppm chlorine band
chlorine - I use powdered dichlor; had trouble keeping it up during yellow algae war; shocked multiple times, mistakenly using di-chlor; used copper algaecide a couple times; chlorine has not dropped below 5-10ppm for weeks now. Just shocked today with a gallon of 6% sodium hypochlorite, which gives me a 10ppm+ reading.

filter condition - during algae war, it would collect slimy build up, but that no longer occurs; some staining remains, probably result of copper treatments; clogging still occurs just about as fast, going from 17psi to 27psi in about a week. Now at 13psi, after rinse, Cascade, brushing, 30 min acid bath, thorough rinse.

unusual conditions, not sure they bear on this, but...the pool is covered with a bubble all winter; this may raise interior air CO2 level to well above normal, which may slow outgassing from pool water (?); I used to keep large rafts on the surface to keep evaporation level down, but stopped using them two months back, thinking the rafts themselves might have been algae-carriers; 10x16 water surface loses about 2 inches every 10 days, surely "helping" to keep CH high.
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Postby Ray1031 » Sat 28 Mar, 2009 15:34

As I said in an earlier post, to me the green tint in the acid after the washing indicates the presence of algae in the filter (live algae). Question ... in your clorine tests are you testing for both total and "free" chlorine in your pool? Live algae is the fastest plugger of pool filters in the book. And pool chlorine can become "bound up". You can, with some of the simpler chlorine test kits on the market find your selftesting only the total chlorine levels in your pool - especially using the off the wall (drop type) chlorine testers. If you use drops to test your chlorine and the indication is in shades of yellow, then you are most likely testing one the total chlorine levels of your pool.

I have seen pools test out for massive amounts of chlorine and is was all "bound" ... the effective "free chlorine" in the pool was negligible/next to nothing. Bound chlorine is "there" and it can affect swimmers and pool surfaces ... but it does no "work" ... it will not attack the things in the pool water it is supposed to. Free chlorine is the chlorine in your pool that is actually working, killing the algae and other contaminants.

If your tester does not differentiate between the two types of algae for you, then I recommend taking a sample to a pool store and getting a free test done. If you have done this and they have not given you both a total and free chlorine reading - take a sample to a different pool store for testing. When in doubt, get more than one opinion. Always!

The only sure method for converting total chlorine to free chlorine is by shocking the pool. With your calcium levels, though it is more expensive, I would recommend using a lithium hypochloride pool shock rather than a calcium hypochloride.

As for your high calcium content ... My first suggestion is: If you use an automatic chlorine feeder with tablets/pucks/sticks ... or a standard granular broadcast chlorine ... or if you normally use floaters or place pucks in your skimmers - Stop! Switch to liquid at least for a while - until you get the calcium under control. Tablet and broadcast chlorines all normally contain calcium. I already mentioned the pool shock - though here too, you can use liguid rather than the granular.

As for lowering the calcium content of your pool, you have two methods: The first is Acid ... Muriatic Acid. If you use a granular ph down you can switch to using liquid muriatic acid instead. Over time it will slowly reduce your calcium levels. The problem here is "time" to do the job quickly you will be drastically lowering your ph repeatedly as you pour in the acid a couple of gallons at a time ... rebuild your ph .... the hit it with acid again ... and repeat until the calcium control is established.

The second method is also a little drastic, though normally quicker and less drastic in the ph and chemical department .... drain about half of the water from your pool and refill it. (Note here: if you have a liner pool "do not" go lower than about ten inches to 1 foot of water in the shallow end or the liner may shift on you ... the same can apply in a high water table area -especially in the spring- as you do not want to risk the pool "floating" on you.)
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Postby Ray1031 » Sat 28 Mar, 2009 15:44

One final thought for you to consider as well .... the results of the filter cleaning and the recent algae problem you were having may be a little slow in resolving your filter issues back to a more normal running pattern.

In many cases after such problems, the pool takes a couple of weeks to actually return to "normal". As I indicated, especially with the mustard/yellow algae, side problems can develop that will clear themselves, but need a little time to do so. You may also find that in a week or two, after things have settled and your pool is acting more normally (chemically) - that your filter will need another cleaning before things finally revert to what is more normal for your pool..
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Postby JPlunket » Wed 01 Apr, 2009 09:12

I use Taylor drop system, which supposedly tests for both Free and Total Chlorine. Since shocking several days ago with sodium hypochlorite, both measures have been "redder" than the 5-10ppm color, no perceptible difference betwteen the two. No problem with algae. Filter seems to be clogging much more slowly than before.

I'm going to acid wash the filter again, then try some of the things you have advised.

Qs: in the muriatic acid approach to reducing Calcium, what period of time between the muriatic acid gallons and "rebuilding pH" (and with what "pH up" chemical?).

Thanks!
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Postby chem geek » Wed 01 Apr, 2009 11:04

You can also use real TSP (tri-sodium phosphate) to clean a cartridge filter as described here . Note that acid washing is only recommended if you have scale deposits and only after degreasing first. In your case, you possibly have scale deposits, but it's good you did a degreasing though dishwashing detergents do not use TSP anymore. Real TSP is more effective at powerful degreasing, though using Cascade is better than nothing.

One key to easier maintenance of cartridge filters is to get one that is oversized for the pool. That way, less frequent cleanings are required. Nevertheless, sand filters are easier to clean, though backwashing does mean using more water.

As for sand filters and use of a Filter Aid, one can also add DE to their sand filter by adding a cup or two to the skimmer (just enough for a 1-2 PSI rise -- you need to wait a bit to see this rise). As was noted with the Filter Aid, you need to add this again after each backwash and it will initially require more frequent backwashing as it catches more particles from the pool water.

For the CYA test, you are supposed to look at the back of the tube, not the front, as shown at the bottom of this link . Halfway between 1.5 and 2 on the front is roughly 80 ppm CYA on the back. You should redo the test to see for sure -- the CYA could be higher as its a logarithmic scale (goes up quickly in that region).

Adding acid will not lower the calcium content in the pool. Adding acid lowers the pH and the Total Alkalinity (TA). The only easy way to lower Calcium Hardness (CH) is with dilution via water replacement with water that is lower in CH. Using rains to overflow is effective for this. Doing a partial drain/refill using fill water only helps if the CH level of the fill water is significantly lower than that of the pool water. Evaporation followed by refill with fill water increases the TA and CH of the pool because evaporation only removes water while the TA and CH in the fill water get added to the pool. Depending on the source of chlorine (i.e. if it's acidic), the TA may be seen to drop over time, but the CH will continue to rise.

With a CH above 500 and a TA of 150 ppm it is true that you possibly have calcium carbonate scale buildup, especially if your pH is also high. You can use The Pool Calculator for calculating the saturation index as well as for dosing quantities. Your high TA is a bit of a puzzle along with the high CYA level. What is your source of chlorine? If it's Trichlor, then that explains how the CYA get high since for every 10 ppm Free Chlorine (FC) added by stabilized chlorine Trichlor pucks/tabs, it also increases CYA by 6 ppm. However, Trichlor is very acidic so usually your TA will be lower and you'll be adding Alkalinity Up (baking soda) to compensate or if the pH is low as well then you'd be adding pH Up (Arm & Hammer Super Washing Soda) which also increases TA. My guess is that you are using Trichlor pucks/tabs and that you are using pH Up to keep the pH up but that increases the TA level.

As for algae, you likely did not keep your FC level higher to compensate for the higher CYA level. In a manually dosed pool, you need to maintain a minimum FC that is 7.5% of the CYA level to prevent algae growth (in an SWG pool, the minimum FC is 4.5% of the CYA level). FC is NOT a measure of the amount of active chlorine (hypochlorous acid) concentration in the water. CYA binds to most of the chlorine so at higher CYA levels you need a proportionately higher FC level to have the same disinfecting, oxidizing, and algae-killing power. This is known science since 1974 as described in the paper in this link . You can read more about managing your pool at the Pool School. If you want to continue to use stabilized chlorine products and not worry about the rising CYA level, then you will need to use a weekly PolyQuat 60 algaecide or a phosphate remover to prevent algae growth, both are at extra cost. Alternatively, you can use unstabilized chlorine, specifically chlorinating liquid or 6% unscented bleach, as your chlorine source and not build up CYA over time, but you will need to add your chlorine every day or two unless you have a pool cover or an automatic dosing system. The only easy way to lower the CYA level is through water dilution (but at least fill water has zero CYA).

Richard

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