# Suggestion for making a small improvement to PoolMath

#### DangerBoy

##### Well-known member

Is this something that could be done? Pretty please?

#### Donldson

TFP Expert
In The Industry
Use "Effects of adding Chemicals" at the bottom of the page to figure out how much CYA you are adding.

Hint: it is a 1-to-0.9 FC-CYA for dichlor and 1-to-0.6 for trichlor. If using dichlor you can essentially treat it as equal amounts, if you are raising your FC by 5 then you are raising your CYA by almost 5 as well. It is close enough for grenades, horseshoes, and the Taylor CYA test precision.

#### Leebo

TFP Expert
The Effects of Adding is also in the Pool Math App in the side menu. Working backwards you’ll see how much to add, but remember, don’t add it all at once.

#### DangerBoy

##### Well-known member
Use "Effects of adding Chemicals" at the bottom of the page to figure out how much CYA you are adding.

Hint: it is a 1-to-0.9 FC-CYA for dichlor and 1-to-0.6 for trichlor. If using dichlor you can essentially treat it as equal amounts, if you are raising your FC by 5 then you are raising your CYA by almost 5 as well. It is close enough for grenades, horseshoes, and the Taylor CYA test precision.
I did that but I thought it would be nice to have the choice of using dichlor or trichlor with the CYA calculator so that's why I put the request in.

There seems to be a small amount of discrepancy between the Effects of adding Chemicals calculator and the CYA calculator. Here's what I mean.

Using the Effects of Using Chemicals calculator I worked out that I need to add a total of 130 g of Dichlor into my 1893 L (500 US gal) tub to get CYA from 0 to 35 ppm. At the same time, I calculated that it would take 66 grams of Stablizer to have the same effect. I then said great, all I have to do is use the CYA calculator and multiply the Stabilizer number I get by 130/66 = 1.9697. To verify this works I then used the CYA calculator to find out how much Stabilizer I'd need to raise CYA from 30 - 35 ppm. The result was 9 g. Multipy by 1.9697 you get 17.7 g Dichlor. BUT if I use the Effects of using Chemicals calc to figure out how much dichlor I need to add to get 5.0 ppm increase in CYA, it turns out to be 18.9 g.

I know that's not much of a difference and using either method will get me close enough for Taylor test kit accuracy so I'm not really concerned about but I am curious as to where the difference is coming from. Is it just rounding error in the calculators? If it's not 1.9697 I should use to convert between Stabilizer to dichlor for CYA effect, what is the exact number I should use?

#### Donldson

TFP Expert
In The Industry
I did that but I thought it would be nice to have the choice of using dichlor or trichlor with the CYA calculator so that's why I put the request in.
My thought is that you are not supposed to add dichlor or trichlor explicitly to raise your CYA. You use those to chlorinate, the CYA is the side effect. So you shouldn't be trying to figure out how much dichlor you need to raise your CYA X amount, you should be figuring out how much dichlor you need to raise your FC to where you want it, and from there you can figure out how much you are raising your CYA each dose. Putting it as an option under CYA might seem nice to you, but the first time we see someone say "I raised my CYA to 50 by adding the amount of dichlor PoolMath told me to" we won't think it's very nice at all...

#### DangerBoy

##### Well-known member
My thought is that you are not supposed to add dichlor or trichlor explicitly to raise your CYA. You use those to chlorinate, the CYA is the side effect. So you shouldn't be trying to figure out how much dichlor you need to raise your CYA X amount, you should be figuring out how much dichlor you need to raise your FC to where you want it, and from there you can figure out how much you are raising your CYA each dose. Putting it as an option under CYA might seem nice to you, but the first time we see someone say "I raised my CYA to 50 by adding the amount of dichlor PoolMath told me to" we won't think it's very nice at all...
Okay, then why does Nitro suggest you start the chlorine in a spa by adding dichor a little at a time for several days to gradually build your CYA level up to 30 - 40 ppm in the sticky post in the Spas and Hot Tubs section (https://www.troublefreepool.com/threads/9670-How-do-I-use-Chlorine-in-my-Spa-(or-pool))? Read the sanitizer section for yourself. I'm just doing what a well recognized expert on this site says to do in a post that was deemed so valuable and informative that it was made sticky in the Spas and Hot Tubs section.

And by the way, I'm not stupid and I do understand what I'm doing. I'm testing for FC every day so I can calculate how much dichlor I need to add to keep my FC up in the correct range. I just need the calculation to figure out when I've cummulatively added enough CYA level to get my CYA level into my target range so that I can then test to see if my level is actually there. The CYA concentration scale on my comparator starts at 30 ppm so there's not much point in me wasting 7 ml of expensive reagent to test for CYA until I've at least got a decent chance of being able to get a reading on my comparator. If I test while my CYA level is still in the teens or 20s, I'll get no result/data from my test and I'll have just wasted a bunch of expensive reagent for no benefit. If I could use the CYA calculator to help me figure out how much CYA I need to cumulatively add to get me to 30 or 35 ppm or whatever I choose, that would be very convenient and useful and I'll be able to minimize my chances of testing for CYA too soon.

If you think people are too stupid to know that they shouldn't try to get to their target CYA level all at once using Dichlor or Trichlor then put a little warning on the calculator telling people not to do that. But anyone who reads Nitro's post to learn about the TFP method will know not to do that. It's pretty clear and easy to understand.