Matt...why is the CDX such a problem with the conversion process? I truly resist draining the pool since I just had it refilled 3 years ago. Why would doing a conversion in mid-season cause such a 'fire-ant' type of scenario in terms of difficulty? I know absolutely nothing about the conversion process other than the small research I've done on it here and from reading a few posts of people who have been through it, but I seem to recall some people here telling me to NOT wait until the following season? I like option 1 much better. I have opened to a green swamp more often than not anyway over the past 28 years. Although opening last year, if memory serves, was amazing. It was practically clear (blue...not green). The previous year was clear...but green. Thus far I'm not encouraged about converting. I didn't anticipate that it's such a major endeavor nor that it would entail any level of drainage.
Just been reading some of these conversion stories. I'm not sure I have the fortitude to accomplish this. 20-50 gallons of bleach needed for a pool around my size? You gotta be kidding me...this process sounds like alot of work. I think I'd really need to personally speak to someone who has converted a CDX/biguanide pool and get some thoughts on it.
CDX is the trade name for an additive that mostly contains a chemical called dimethylhydantoin (DMH). DMH is often used in bromine hot tubs as it helps, in a very ineffective way, to stabilize active bromine levels. DMH also stabilizes peroxide levels which is why it is used in the Baquacil system - it helps to moderate the fluctuations in Baquacil oxidizer levels. The problem with CDX is that the DMH interferes with chlorine's ability to oxidize the biquanide sanitizer making the conversion process last A LOT longer than it should.
In a standard baqucil pool with no CDX, the conversion of baquacil by chlorine is basically nothing more than chlorine oxidizing the biguanide polymer (creating some very interesting water colors). This oxidation process produces many different chemical intermediates that turn into a goopy polymer residue that we often refer to as baqua-goop. The goop can be skimmed off the top of the pool and anything that settles to the bottom can be vacuumed up and sent to the filter. As you might imagine, this makes a mess of standard sand filter and, at the end of the conversion process, requires a sand change because there's no effective way of washing the sand clean of all the residual baquacil. Since sand is cheap, the one-time replacement is a minimal price to pay for an easier pool to take care of long-term.
Yes, the conversion process can require as much as 50 gallons of bleach because the oxidation process consumes a lot of chlorine. When biguanide levels are low, as they often are in spring time, the chlorine demand is a lot lower since there is less biguanide to convert. If one tries to convert a pool mid-season when the sanitizer levels are at their recommended concentration, the conversion process requires a lot more chlorine. This is why conversions are best done at the beginning of the season.
The reason why this process can be painful is because the first few days literally require you to be pool-side baby-sitting your pool. The initial doses of chlorine bleach will all be consumed after the first few minutes of pouring it in. Because the free chlorine levels need to reach 15ppm, the initial conversion requires adding chlorine, allowing it to circulate and then measuring and dosing to try to achieve 15ppm. It can take 24 hours or more before the pool will start to hold any measurable level of chlorine. During that time, the filter will begin to load up with baqua-goop and the pressure will spike. This will then require backwashing to restore pressure and flow. In many cases, I typically advise people to put their filters into recirculate mode for several days and to manually scoop out the degraded polymer as that is more effective than loading up a filter. Then, when they're just dealing with water cloudiness, put the filter back into service and use that to help clear the microscopic particulates.
CDX, of course, makes the above process even longer. So, in some respects, it is just easier to drain the pool and get rid of most of the CDX that way and then do a quicker conversion as you'll only be dealing with the little residual water in the plumbing system that has baquacil in it. In you case, given all of the chemicals you have added to your pool to try to solve your water mold issues, I really think draining is the best option. Yes, draining a pool is a huge hassle and requires careful planning to do it right (as well as the expense of paying for water), but it would make converting YOUR pool much easier.
As always, it's up to you. I really don't you'll enjoy trying to convert your pool now that it is mid season....I certainly would not want to do it.
