Inline Versus Offline Chlorinators
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When it comes to dissolving chlorine pucks into your swimming pool water a lot of pool owners simply put them right into the pump or skimmer strainer baskets. Please do not do this as it will absolutely cause damage to your plumbing lines, your skimmer and potentially all of your pool equipment. Quite possibly costing your many thousands of dollars in extra (and early) repair costs. Here is an article where I talk more about the concerns with this and why you should never put chlorine pucks into your skimmer.
The device made for dissolving chlorine pucks (safely) into your pool water is called an erosion feeder. It is a very inexpensive piece of equipment which gets installed as the very last component on the equipment pad right before the water is returned to the pool. This is the safest location to inject chlorine into your pool water to ensure that you do not damage your pool equipment from the concentrated chlorine. However, there are a few kinds of chlorine erosion feeders on the market and it is important to choose the right one. There are both different forms of erosion feeders (inline and offline) but there are also different types of erosion feeders for different types of chlorine (stabilized versus unstabilized) so this can get a little confusing to the uninitiated...and chlorine can cause a chemical explosion if you use the wrong type or the wrong kind of erosion feeder so the stakes are pretty high. Let's clear up some of the confusion here:
Stabilized versus unstabilized chlorine pucks - Chlorine can come in stabilized pucks or unstabilized pucks. These are NOT interchangeable in any way. Stabilized chlorine has CYA (cyanuric acid) added to the pucks to help them to dissolve slowly and in a controlled fashion. When these pucks dissolve and add chlorine to the pool they are also adding CYA to the pool in an almost 1:1 part per million ratio. This causes CYA to build up quickly and to problematic levels so some pool owners choose not to use stabilized chlorine pucks for their main chlorine dosing option. One alternative is unstabilized chlorine, which can come in liquid, granular or also pucks / tabs. If you want to use unstabilized chlorine pucks like cal-hypo chlorine pucks, then you need to have a dedicated erosion feeder purpose built for these unstabilized chlorine products.
Never mix and match chlorine products. If you add unstabilized chlorine pucks to an erosion feeder designed for stabilized chlorine this will cause a violent chemical reaction and explosion. Even residual values of one chlorine type in a container can react with other chlorine, and so you can never mix and match chlorine containers, scoops, or especially erosion feeders!
Offline erosion feeders - Of the two kinds of erosion feeder for stabilized chlorine pucks you will have the option to choose an inline or an offline version. While both of these erosion feeders are suitable for dissolving chlorine into your pool, there is a definitive advantage to the offline version. Instead of forcing the entire flow of your system through a bottleneck at the erosion feeder, an offline erosion feeder uses differential pressure created by the filter to create a slow feed syphon which passes water over the chlorine pucks and doses it into your pool system. There is no filtration choke point with an offline chlorinator so all things being equal these would be the preferred style versus inline erosion feeders.
Inline erosion feeders - Inline erosion feeders are slightly more common than offline ones, and I suspect that they might work a little better also to ensure even flow of water over the chlorine pucks within them...but at the expense of being a fairly extreme resistance to flow. Very large and commercial swimming pools likely use this style of erosion feeder but for the average residential pool I would encourage to use offline feeders. Forcing the entire flow of your filtration system through the chlorinator adds substantial resistance to flow which can be avoided with other chlorine feed options.
There are no black and white, right or wrong ways to build and install a pool filtration system. However you should want to design a system which is functionally efficient and minimizes waste energy losses. This is why if you must use stabilized chlorine pucks for your pool it would be an advantage to choose an offline chlorinator versus an inline chlorinator. Something like the Hayward CL220 (offline) instead of the Hayward CL200 (inline) would make your system more efficient and less dynamic head (resistance to flow).
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Swimming Pool Steve is an award winning, second generation swimming pool specialist from Ontario Canada and one of the most trusted voices in the swimming pool industry. With over 20,000,000 views on the Swimming Pool Steve YouTube Channel, winner of the Pleatco Pool & Spa Industry Leadership award and author of hundreds of pool and spa articles both online and in print. Steve is committed to helping pool and spa owners as well as pool and spa industry workers learn more about the technical side of building, renovating, repairing and maintaining all types of swimming pools and spas. Follow Swimming Pool Steve on Facebook, Twitter and YouTube.
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