Quote Originally Posted by CarlD View Post
Sunny,
You really need to check your information before giving out advice.
Now, now, just trying to be a nice and helpful member of the community here...but if you want me to be more specific with fact-checking, how's this -

I've never heard that if FC is 10 or higher that CYA cannot be measured. I don't know where you got that from and I would never advise it.
Based on my experience with testing CYA at high FC. Got false low readings. Already explained that in a previous reply. Since that was a personal opinion, I'm totally willing to retract it. Just because I had some off measurements at high FC doesn't mean others will.

Further, what high FC DOES do is cause pH readings to appear high--that's why you need to use the R-0014 for the pH test, not the R-0004 when the FC is 10 or higher. If your FC is, say, 30 and your pH is 8, then trying to drop your pH to 7.2 will actually drop it far lower PUTTING YOUR LINER AT RISK!
Couple of things to refute here.

First, both the R-0014 and R-0004 are the same chemistry - Phenol Red (links to MSDS's are HERE and HERE). The only technical difference between the two is that they have different phenol red concentrations and they use slightly different color comparator blocks. The R-0004 is what is shipped and used in all K-2006 test kits.

When FC is above 10ppm but below 25ppm, Phenol Red starts to convert into Chlorphenol Red. The Chlorphenol red is an indicator for lower pH (somewhere down at 3 or 4, I believe) so a fraction of the chlorphenol red turns purple colored and causes a false high reading. Above 25ppm, the conversion of phenol red to chlorphenol red is almost fully completed and thus makes the pH indicator useless.

Second, I never stated that the OP should adjust his pH based on false values. I was specifically cautioning against that.

You can also add a couple of drops of chlorine neutralizer before you test.
You SHOULD NOT use the sodium thiosulfate chlorine reducer to take down the FC level prior to pH testing. There is a good discussion of that HERE with pictures in this thread showing how the thiosulfate changes the color of the pH indicator for the same water samples. The thiosulfate Cl reducer is both alkaline in nature and it's reactions with Cl raise the pH of the solution by an unknown amount thus making the subsequent phenol red test result invalid.

The only way to test for pH with an FC between 10ppm and 20ppm is to dilute the pool water sample with DISTILLED water as the distilled water has a pH of 7.0 and no alkalinity. Therefore the pool water's alkalinity can buffer any pH change from the distilled water addition while allowing the dilution to reduce the FC level.

A rigorous technical discussion of ways of reducing the effects of chlorine on phenol red pH indicators can be found HERE

Then you give advice to raise FC to the shock level. How do you know what the shock level is if you can't measure CYA with FC at 10?
Nice rhetorical trick but you're twisting my words. The OP stated that his CYA was 30 (or maybe it was 40), so you go based on that number and do an accurate measurement of CYA later.

Further, one does NOT need to add chlorine every 2 hours when fighting a bloom. Testing and adding chlorine 3x/day is enough.
We all fight our algae blooms differently. If you have the time to do it every two hours, then keeping the chlorine level at or above shock level helps enormously because it doesn't allow the algae to get a foot hold. Algae double their population sizes roughly every 3-8 hours (see posting HERE), so you need to keep your FC at or above shock levels in order for the kill rate to be greater than the growth rate. HERE IS A LINK on the various kill rates of chlorine for different pathogens. The column labelled "CT factor" (chlorine concentration multiplied by kill-time) lets you compare the relative effectiveness of chlorine on different pathogens (low CT factors are good).

Being experienced, you know as well as I do that the concentration of FC in your water volume is variable from top to bottom and from well-mixed to stagnant spots. Algae concentrations and colony sizes also vary from place to place in a pool. As well, chlorine kill times are typically measured in controlled Petri dishes where the pathogens are not free-floating in a giant volume of water (meaning the effectiveness of chlorine in you pool is not the same as chlorine in a Petri dish). So the best bet is to maintain your FC above shock levels as best you can. If you happen to have a day-job, then you just do your best and maybe seek the assistance of a friend, family member or neighbor's kid to help you out.

I would advise that these types of treatments be started on the weekends (starting on a Friday) as it allows the pool owner to concentrate on the task at hand and really get a good go at it. A little bit of planning and proper chemical preparation can really make the process quite easy to pull off.

Brushing "a lot"? Brushing and vacuuming (to waste, not to the filter) once a day should be sufficient--and it's plenty of work as it is!
See above, to each his own. Brushing helps mix the water column (especially if you have one of those Whale-Tail brushes) for better chlorine distribution and also mixes up the dead algae in the pool so the filter can work on it. If you can vacuum to waste, that's great but not always feasible - depends on your equipment setup and if water replacement is expensive in the region you live in.

While an algae bloom is a pain the lower extremities, it is still possible to clear it up easily without working oneself to a frenzy. If you work, you cannot be checking and adjusting FC levels every 2 hours. The whole idea of our systems is to keep things as simple as possible.

We have more than one stickied thread on how to clear an algae bloom. It's not hard and you don't have to drive yourself crazy. You DO have to be consistent and persistent.
Never been frenzied or crazy in my life...