Daily FC testing -- what to use?

[JasonLion]

singerteacher, it is possible to learn what a FC level of 6 looks like on a standard OTO test without dilution by comparing what you see to a FAS-DPD test a number of times. But it won't look like any of the color blocks on the color comparison chart that comes with the OTO test and many people have trouble telling the shades of yellow apart even with practice. The different yellows are distinct, but without a color reference it is tricky to figure out.

I really think that you can figure out a standard amount of chlorine to add each day, by experimenting for several days with the FAS-DPD test, and then use that amount for several days before rechecking how things are going with the FAS-DPD test. On the days you are not using the FAS-DPD test, a quick OTO test is good enough to tell you if things have gone significantly wrong, even if you can't distinguish the shades of yellow. If the OTO test looks off in any way then you can confirm with the FAS-DPD test.

If you are worried about being sure to keep FC at 6 or above, you can simple aim for a slightly higher level than that when figuring out your daily chlorine addition. With a little extra attention when there is a swim party or major storm, it really is possible to have consistent FC levels even without daily testing. FAS-DPD testing is important at least once a week so you can adjust things as the seasons change.

 

[chem geek]

I will buy an OTO kit and aim at keeping FC at 5ppm. That should be okay, right? I really don't want to get algae again ... and I'm getting it when my FC goes under 4ppm.

So I just want to be clear. When the FC drops below 4 ppm with your 50 ppm CYA you start to get algae growth, is that correct? And this algae growth is green algae or is it yellow/mustard algae? From your previous posts it sounds like you got rid of green algae a little over a week ago, so was your FC just below 4 ppm at that time which is why you are saying that's when algae starts to grow in your pool?

I noticed that you got this pool last year when you bought a foreclosed house and it was in pretty bad shape. You might consider doing water dilution over time. If you have a sand filter you regularly backwash then that will help as will using rain overflow. I'm just thinking there might be years of accumulated junk in the pool that could cause strange chemical issues like higher-than-normal chlorine demand or tying up chlorine (similar to what CYA does) making it less effective against algae, etc. This isn't urgent, but more of a long-term strategy to get your water back to being "fresh". Even in my own pool, I use winter rains to dilute the water, but that's mostly to keep the salt from building up to much over several years. Normally chlorine does a fine job getting rid of chemical contaminants, but given enough time and enough history of who-knows-what the previous owners threw into the pool, there could be things in the water that chlorine doesn't deal with very well or that interfere with chlorine's effectiveness.

Another option to consider is having 50 ppm Borates in the pool as this can act as a weak algaecide. I'm going to do an experiment at the end of this season to see how long my pool will take to turn dull with no chlorine now that it has 50 ppm Borates in it (without the Borates, it "turns" pretty darn fast), but my lower chlorine usage seems to indicate that it at least takes the "edge" off of algae growth.

Richard

 

[singerteacher]

I really think that you can figure out a standard amount of chlorine to add each day, by experimenting for several days with the FAS-DPD test, and then use that amount for several days before rechecking how things are going with the FAS-DPD test.

With a little extra attention when there is a swim party or major storm, it really is possible to have consistent FC levels even without daily testing. FAS-DPD testing is important at least once a week so you can adjust things as the seasons change.

Last season, I used the dip stick tests to figure out when to add chlorine and it was a disaster. I now realize that my readings were way off. So far this year, I've been using the FAS-DPD test nearly every day in an attempt to figure out chlorine usage. I don't think I've got it figured out yet, though, and I really need to test nearly every day until I have a better idea. For example, earlier this summer we had a huge windstorm which dropped a whitish dust and pollen in the pool, which was basically invisible except for some funny-looking pods in the skimmer sock. Meanwhile the dust/pollen was invisibly consuming my chlorine at a rapid pace. The water didn't start to look yellowish until the algae had already gotten hold. I wasn't testing every day, and was thinking that since it was cloudy and cold I could use my "cloudy day" amount. That experience has led me back to testing ... along with my unfounded fears of yellow algae!

I don't feel very confident about how much bleach to add daily yet. I've ordered the T-1000 and will use that this summer, and hopefully by the end of the summer I'll be able to guesstimate how much bleach to add based on various conditions like sun, clouds, leaves, parties, and pollen. Basically, it's almost like I just got the pool, because last summer was so confusing that I didn't learn anything about my chlorine usage except that the dipstick tests aren't accurate! I'm determined to get a grip on it this summer.

 

[singerteacher]

And this algae growth is green algae or is it yellow/mustard algae? From your previous posts it sounds like you got rid of green algae a little over a week ago, so was your FC just below 4 ppm at that time which is why you are saying that's when algae starts to grow in your pool?

Another option to consider is having 50 ppm Borates in the pool as this can act as a weak algaecide. I'm going to do an experiment at the end of this season to see how long my pool will take to turn dull with no chlorine now that it has 50 ppm Borates in it (without the Borates, it "turns" pretty darn fast), but my lower chlorine usage seems to indicate that it at least takes the "edge" off of algae growth.

Richard

It's not mustard algae -- FC does not drop at all overnight and CC is zero. I was attempting to hold my FC at 3ppm when I got the green algae, although we got a big pollen/dust dump and that dropped my FC under 3ppm until I quickly bumped it back up. But, actually, I don't have any real proof that algae grows every time it goes under 4ppm, just that holding it at 3ppm doesn't work, or at least doesn't give me a big enough margin of error to deal with overnight pollen/dust storms, etc. I was very surprised to read that I should maintain FC at 6ppm. Not sure where I got the 3ppm idea -- I'm thinking it was the Taylor test kit booklet!

My CYA has dropped since last summer (60 then, 50 now) due to all the backwashing I did last summer. I think it will keep dropping since I'm still backwashing quite often and it has been raining here for a week now.

The previous owners left us a crazy assortment of chemicals, so who knows what is in our pool that could be hurting our chlorine usage. I hadn't thought of that. (Sheesh! We already had to replace the pump, repair three leaks, get new heat sinks ...) I'd like to read more about borates, and their potential to hold chlorine. How do you test for them? Maybe I already have them?

 

[Guest]

Here is a bit of practical experience. Here in Florida during the summer my customers with 50 ppm CYA had no problems when they maintained their FC between 3-5 ppm. Under 3 ppm was a problem. What you are saying is not inconsistent with this. The FC/CYA chart is based on more theoretical than practical data and tends to be a bit conservative. There is actually a bit of leeway. If you follow it you should not have any problems but if your FC is a bit lower then you should not have any problems either.
Remember, your chlorine is going to fluctuate and is not a constant during each day.
This is not "carte blanche" to get lazy with your testing and maintenance but merely a reminder that you really don't have to micromanage your pool and should spend most of your time enjoying the water instead of stressing over it!