How long should it take a 20,000 gallon pool to use ten of the 3" chlorine tabs in the dispenser attached to the pump/filter?

July 23, 2008 9:18 AM

How long should it take a 20,000 gallon pool to use ten of the 3" chlorine tabs in the dispenser attached to the pump/filter?

The pump runs for 8 hours a day (it's July and it's in Texas)

One website I found says" Tabs are 3" diameter and weigh a full 8 oz.Last up to 7 days in pool. 1 tablet per 10,000 gallons of water"

Does that mean 1 tablet in 10,000 gallons lasts 7 days, or the full dispenser should last 7 days? I'd think if I put 10 tablets in my feeder for my 20 gallon pool, they should last about 5 weeks.

Is this accurate? Can you all who have pools and use these 3" dispensers let me know how quickly you go through the tablets?

On a related note, if anyone in Plano TX or the surrounding Dallas area can personally recommend a cleaning and maintenance service that isn't full of you know what, please do so.

posted by jesirose to home & garden (16 comments total)

Well, this may be obvious, but just in case it's not.... If you put in all 10 tablets at once, they will last for 7 days. If you put in 2 (1 per 10,000 = 2 per 20,000), and replace every 7 days, you should indeed get 5 weeks out of the pack of 10.
posted by Grither at 9:36 AM on July 23, 2008

Oh wait, I just noticed that you said "feeder", so perhaps you have some contraption that uses them up as necessary? In that case, you might be getting less than 7 days out of the tabs for a variety of reasons like pump speed, frequency, water temp, etc...
posted by Grither at 9:41 AM on July 23, 2008

Grither, we have a "feeder" attached to the pump. In theory it is supposed to dispense them as needed, otherwise why would it be big enough to hold 10? Then the pool would have WAY too much chlorine.

It is this model: http://www.bestbuypoolsupply.com/320chlorinator.html

It says it "Holds approximately [...] 11- 3 " chlorine tablets."

I am not the one who put 10 of them in, but I would think if you filled it up the "automatic" part would imply it would only use what is needed over the 7 days, so it would automatically use 2 tablets a week for my pool. However, the person who did put 10 in says he put them in on a Tuesday and the next Friday my husband looked and it was empty.

So either he lied about putting them in, or it used all 10 in a few days. I am inclined to think the first, but I don't know enough about the pool or equipment (which is why I pay the people to do it for me).
posted by jesirose at 10:05 AM on July 23, 2008

Grither's first answer is correct. 10 will last no longer than one.

Go online and sign up at one of the many pool forums. Do some reading on the "BBB" method of pool maintenance. I have a 15,000 gallon pool and it costs me about $1 (and about 5 minutes) a day to maintain it using nothing but liquid chlorine, borax, and baking soda. It's been crystal clear and trouble free since day 1.

Consider getting a Liquidator. It's an extremely simple, inexpensive, and do-it-yourself chlorine dispenser that uses standard liquid chlorine. It will pay for itself very quickly. I have one. It's awesome.
posted by Patapsco Mike at 10:05 AM on July 23, 2008

Saw your follow-up. The "dispenser" is nothing but a container that your pump runs water through. It doesn't have any way of knowing if you have no pucks or 10 pucks in there. If it has a 1-10 setting, you might be able to dial it down below 1 and get an extra day or two out of your chlorine tabs, but basically it's something a pool service installs to get you to buy their pool chemicals. It is there to get you to spend more money at the pool store.
posted by Patapsco Mike at 10:10 AM on July 23, 2008

The pool came with the house, so I personally didn't choose the feeder. So the only reason it holds 11 tablets is so you can over-chlorinate the pool and use too many, thus buying more? That seems like a HUGE scam, and bad for the pool.

It does have some sort of dial on the side. I don't see any numbers, maybe they wore off.

I have other reasons to distrust the current pool service so that is why I am so quick to assume he did not put 10 in. But if he did put 10 in, that seems like a stupid thing to do if they are just going to get used up - since the pool service is supposed to supply their own tablets. So they'd be costing themselves more money.

I'll read about the BBB method, thanks. We are looking into hiring a new service because it's not just the chlorine that needs to be done but everything, the cleaning of the walls, the filter, etc. But I will definitely check it out.
posted by jesirose at 10:19 AM on July 23, 2008

I don't think that feeder works the way you think it does; we have a similar device attached to our pool, and in operation it fills completely with water so all the tablets inside it dissolve at the same time. The dial on the side seems to be mostly for show, I've never noticed any difference no matter where I set it.

I would suspect that your pool is extremely overchlorinated right now.

I throw in one or two 3" tabs every couple of weeks, whenever I remember to; they dissolve faster than that, and the chlorine level in our pool is usually much, much lower than the 'recommended' amount -- it barely registers on the little test strips -- but that still seems to be plenty to keep the thing clean and clear. (I don't know if this is because it's indoors, or if we just have naturally cleaner water than usual, or because nobody's peeing in it, or what... but it doesn't seem to take much chlorine at all to keep things from getting ugly.)


You should consider learning how to maintain it yourself, rather than dealing with maintenance companies; it's really pretty easy to do and doesn't take much time at all. (I only have to sweep the walls and floor once or twice a year; backwashing the filter is a matter of flipping a couple of switches, and after a couple tries you'll get a feel for how much your water needs to be pH balanced and in which direction and won't even have to measure carefully.)
posted by ook at 10:28 AM on July 23, 2008

Then why the hell does it hold 11!

Our pool is outdoors, and if the walls and floors don't get brushed they get very gross. Right now the pool is over chlorinated and we still have a small bit of green algae on the side. Is the chlorine making the algae grow? I thought it kills it.

I'm going to go post on a forum because this has just led to more questions. And now I'm pissed off about this stupid feeder that holds 11 tablets when it doesn't do anything automatically at all.

The books I got on pool maintenance make it sound much harder than just flipping some switches. :(

Stupid pool.
posted by jesirose at 10:54 AM on July 23, 2008

http://www.poolforum.com/pf2/showthread.php?t=1113

The above link is a great place to start. All it takes is some common sense and a few hours to study the basics. It will sound like a lot at first, but that's only because they try to cover absolutely everything. You will quickly figure out that 90% of the stuff they talk about won't be of concern to you. What the site will do is help you figure out which 10% of the stuff you really need to keep an eye on.
posted by Patapsco Mike at 10:54 AM on July 23, 2008

jesirose writes "So the only reason it holds 11 tablets is so you can over-chlorinate the pool and use too many, thus buying more? That seems like a HUGE scam, and bad for the pool. "

In defence of the feeder supplier they could make feeders in one puck increments such that a feeder would be appropriately sized for each individual installation. This requires at least 11x as much shelf space as making a feeder in the largest size required and allowing the customer to just put the right number of pucks into it when filling.

Heck it's possible feeder manufactures do make them in different sizes but supply houses and service companies only stock a couple. You've only got so much space in your truck and the customer doesn't want to pay for you to be running back and forth for the exact right thing in most cases when a more universal part will work with a little training.
posted by Mitheral at 11:07 AM on July 23, 2008

The reason the feeders are big is because they want to sell you all sorts of things to put in them. I suspect the pool chemical manufacturers and dealers have dreams where every week, every pool user uses three chlorine pucks, two "ultra clear" pucks, one copper herbicide puck, and one "super mineral" puck. I am not making those up. You can buy all kinds of "make your pool amazing" crap to put in there. But you don't really need any of it- other than the chlorine which is 1/5 the price if you buy it in liquid form.

if you don't believe me
posted by Patapsco Mike at 11:21 AM on July 23, 2008

Makes sense Mitheral.

However, I'd expect the pool maintenance guys to know that, and not put 10 of them in for a 20,000 gallon pool if it should only use 2 a week. As I said the pool came with the house so we didn't get any training except what I have read in books and online, and this is the first that I have heard that it's not supposed to be filled - because the guys that maintain it fill it up! lol.
posted by jesirose at 11:23 AM on July 23, 2008

I agree it's overwhelming at first, it took a while before I felt confident in what i was doing, and I had a few goofups along the way. I can certainly relate to the "stupid pool" feeling :P But it gets easier; most of what's in those books isn't going to be relevant, as patapsco mike says.

On the other hand, clearly the pool maintenance people don't always know what they're doing either, or that guy wouldn't have stuffed eleven tabs into that feeder. (I can only assume they make them that large so they can be used on olympic-sized pools too?)

The chlorine should kill the algae, though if there's a lot it can take a while. (But... if what you're seeing is bright green water that's not cloudy, it's likely copper instead of algae -- if the water gets overchlorinated and out of pH balance it can start dissolving the copper in the heat exchanger. (That was one of my goofups; I kept dumping in more chlorine, wondering "why isn't this killing that algae?" when in fact I was just making it worse.) If that's what's happening, it can damage the heat exchanger if you let it go too long.)
posted by ook at 11:24 AM on July 23, 2008

ook thanks for the reply. Yeah I basically get that the chlorine and pH should be at such and such levels, the stuff that I don't want to deal with is the pump and filter, etc.

The algae I speak of is attached to the wall, around a light, not floating in the water. It's dark green not bright. Does that sound like algae still? It's a few spots around it. However since the pool has so much chlorine and the spot is relatively small, it would make sense that it is something else.

I don't know what a heat exchanger is, but our pool isn't heated by anything other than the sun ;)
posted by jesirose at 11:37 AM on July 23, 2008

Yeah, I'd assume that's algae or something similar; not a chemical problem, anyway. If it's adhered to the wall you may have to brush it loose so the filters can get at it, or vacuum it out -- chlorine will kill it, but won't dissolve it.

our pool isn't heated by anything other than the sun ;)
Ha -- if we tried that, I'd have a skating rink, not a pool :)
posted by ook at 12:41 PM on July 23, 2008

The reason that the pool has a bigger dispenser than it needs is that the amount of chlorine it's using is always changing. Some of the factors involved are water temperature, water chemistry, amount of sunlight, amount of pool use, and whether or not anything (like algae) is growing in your pool. I have a 15,000 gallon pool myself and my use has ranged from one 3" chlorine tablet every 10 days during the middle of winter, to one 3" tablet every day during a particularly nasty attack of algae in peak season.

In defense of your pool company, they may be keeping the chlorine level high on purpose (called superchlorination). As I found out the hard way, a little bit of algae can turn into a swampy nightmare in a matter of days. The best way to deal with it is to get on top of it right away by upping the chlorine, scrubbing regularly, and maybe adding some algicide. Algae can be pretty resistant to chlorine, my pool's infection took over twice the maximum amount you can safely swim in before it died. It may seem like they're adding an obscene amount of chemicals, but in the long run it takes a lot less if you zap it right away.
posted by TungstenChef at 2:22 PM on July 23, 2008