NST Prime tablets turning skimmer and exhaust brown or black

[rackflot]

Hello.

I have been using the poolife® Brite Stix® Sanitizer system for years. I finally ran out and went to get more. The pool store said this was discontinued and to go to the NST Prime system. Just another bucket of bricks. Ok so I did.

Now i see that the skimmer where i put the tablet is turning black where the tab sits along with the throat of the skimmer. It can be wiped off but is difficult to remove and seems to build up. The exhaust port in the pool is turning brownish yellow now.

The white cylindrical bright sticks never did this and the pool has been trouble free for years.

Is it the NST tabs?

 

[reggiehammond]

Tabs shouldn't be placed in skimmer - you're sending concentrated, acidic water directly to your pool equipment. No idea where the discoloration is coming from but the tabs are a good guess.

TFP doesn't recommend tabs because you're always adding CYA. Do you have a recommended test kit?
Test Kits Compared

 

[Rancho Cost-a-Lotta]

Welcome!

The first product is dichlor with copper. The second product listed is calcium hypochlorite (NST/non-stabilized tablets). Dichlor and cal-hypo should never be combined. What you're seeing in the basket is probably a reaction between the two forms of tablets along with the copper.

Neither of these products is a sustainable form of chlorination. TFP recommends liquid chlorine bleach or a saltwater chlorine generator.

Check out Pool Care Basics.

 

[JoyfulNoise]

That is copper precipitation. You probably have a significant amount of copper built up in your water. NST tablets are calcium hypochlorite which is a very caustic substance and causes the pH to increase in the very confined space of your skimmer and plumbing. This is why the plastic is turning black - copper oxide is depositing on it, on the interior walls of your PVC plumbing and eventually at the wall returns.

You should have your pool water tested for copper metal, it’s probably high enough that you need to drain a significant amount of water from the pool.

 

[JoyfulNoise]

Tabs shouldn't be placed in skimmer - you're sending concentrated, acidic water directly to your pool equipment. No idea where the discoloration is coming from but the tabs are a good guess.

TFP doesn't recommend tabs because you're always adding CYA. Do you have a recommended test kit?
Test Kits Compared

NST’s are made of cal hypo. They are caustic/alkaline, not acidic. The Brite Stix are made of dichlor which is only mildly acidic but does contain CYA. The two solids should never be in contact with one another but it’s probably not a big deal if one uses NST after having used Brite Stix because the chemical is almost certainly flushed out.

The black reaction is copper oxide scale.

 

[rackflot]

ok, I really don't like those tabs. I agree there could be a chemical reaction.
The tabs don't go in the skimmer, are they meant to be a floating device twhere they are just exposed to the water?

So what is the protocol for using liquid Chlorine?
I do add and Algaecide once a week along with the blue liquid clarifier

My pool is 18ft round, 52 inch depth.

 

[Rancho Cost-a-Lotta]

Take a look at the Pool Care Basics link I posted above. TFP does not promote the regular use of algaecides. Many contain copper but, realistically, if pool balance is properly maintained, there's just no need for it. Pool clarifiers are unnecessary, and can clog up filter.

One of the cornerstones of TFP pool care is self testing with a TFP recommended test kit. The test kits from Tftestkits.net provide the best value (Test Kits Compared)

Liquid chlorine is one of the sanitization methods recommended by TFP. The other is the use of a salt water chlorine generator. Download the PoolMath app for guidance on the amount of chemicals necessary.