Squeeze last bit of life out of cell?

[JoyfulNoise]

The iron stains come from the SWG causing the iron to precipitate. Iron oxide will come out of solution as a very fine, microscopic precipitate that builds up over time on surface. White plastics and fiberglass are especially susceptible because the participates can develop a slight surface charge to them and they will then be electrostatically attracted to the polymer surfaces. That’s why you see a gradual yellow then brown build up. It’s likely in your municipal water from old iron pipes (that’s why the use zinc orthophosphate corrosion inhibitors).

You just want to keep an eye on PO4 levels. If they start getting above 3000ppb, you may need to knock them back down to avoid algae growth.

 

[Saturn94]

The iron stains come from the SWG causing the iron to precipitate. Iron oxide will come out of solution as a very fine, microscopic precipitate that builds up over time on surface. White plastics and fiberglass are especially susceptible because the participates can develop a slight surface charge to them and they will then be electrostatically attracted to the polymer surfaces. That’s why you see a gradual yellow then brown build up. It’s likely in your municipal water from old iron pipes (that’s why the use zinc orthophosphate corrosion inhibitors).

You just want to keep an eye on PO4 levels. If they start getting above 3000ppb, you may need to knock them back down to avoid algae growth.

More great info! Now I better understand what is going on. You’re the first person who has been able to explain to me what is happening….thank you!

Algae growth above 3000ppb? Since I starting maintaining proper FC levels for the CYA level (I first learned this from Ben on Pool Forum a long time ago, probably 14 years ago?), the pool has never had an algae breakout (and with a solid tarp over the mesh cover when closed, the water is always clear at opening).

Since algae growth isn’t an issue for me, would you still recommend I knock down phosphates if they get above 3000ppb? If I treat for phosphates, does that also remove the Jack’s Magic sequestrant (I’m thinking yes?).

Again, thank you. This is very educational and a big help.

 

[Saturn94]

UPDATE:

I’m getting ready to close so did a full suite of tests, including salt using various methods. The new T15 cell I bought earlier this season has been performing normally.

As suggested by Joyful, I reduced usage Jack’s Magic Purple Stuff, but still enough to keep staining under control.

Here are the salt results (water temp 70°):
SWCG Average salt reading: 3000
SWCG Instant salt reading: 3000
Electric salt meter: 3280
Salt test strip: 3230
Taylor K1766 drop test: 3400

So, the delta has tightened up quite a bit. At least now everyone is in the same ballpark. I found it interesting the salt meter and strip are nearly identical.

 

[JoyfulNoise]

You can achieve better resolution on the K-1766 salt test by using a 40mL water sample. In that case, each drop of titrating reagent is 50ppm [NaCl].

 

[JamesW]

You can achieve better resolution on the K-1766 salt test by using a 40mL water sample. In that case, each drop of titrating reagent is 50ppm [NaCl].

I use a 2 liter sample size where every drop is 1 ppm.

I suppose 50 ppm resolution is ok, but I like to be really sure.

 

[JamesW]

SWCG Average salt reading: 3000
SWCG Instant salt reading: 3000
Electric salt meter: 3280
Salt test strip: 3230
Taylor K1766 drop test: 3400

This is the most reliable way for salinity.

By doing multiple independent tests, you can increase the probability that the tests are really close to being accurate.

 

[Saturn94]

I use a 2 liter sample size where every drop is 1 ppm.

I suppose 50 ppm resolution is ok, but I like to be really sure.

 

[Saturn94]

You can achieve better resolution on the K-1766 salt test by using a 40mL water sample. In that case, each drop of titrating reagent is 50ppm [NaCl].

I take it with a 40ml sample I would still only use 1 drop of chromate indicator (R-0630)?

 

[JamesW]

I take it with a 40ml sample I would still only use 1 drop of chromate indicator (R-0630)?

For 40 ml, I would use 2 drops.

Realistically, a 20 ml sample with a 100 ppm resolution is the most that would be reasonable.

 

[Saturn94]

….. Had I known this last year, it would have saved me a lot of frustration and expense.

Interesting update….

In an odd twist of fate, buying a new salt cell last year saved me a bit of money. Last year the T15 cell was $650, now it’s $899!!!

 

[Newdude]

+1. I was ticked to go through all that trouble getting pool equipment last year when my build didn't happen. It's just as scarce this year and a few hundred more each piece.

 

[JoyfulNoise]

Likewise here. I replaced my original IC40 with an IC60 last May. Had I waited one more season the sticker shock would have been 10X worse… but then again everything is nuts. I just paid $12 to eat a sub and a pickle at JimmyJohns … just me

 

[Saturn94]

… but then again everything is nuts…

So true!!!

I just looked….in 2015 I bought genuine Hayward T15 cell from Amazon (not an Amazon Merchant) for $398. In 2021, $650 (Leslies online), in 2022 they are $899 from a variety of reliable sources.