What happened? Sky high pH & FC; black/metallic residue below waterline.

[NathanielT]

Four-year old spa. Used sparingly, maybe 2X month.  After a week or so of non-use, opened the spa to see black / almost metallic residue all over, and not right along the surface.  It seems to come off with a magic eraser, albeit not easily.  Testing with Taylor K-2006 test kit shows:

Free Chlorine -- too high to measure (turned and stayed dark pink after one scoop of DPD powder 870 despite 30+ drops of 871)

Combined Chlorine -- couldn't measure

pH -- well above 8.4

TA -- also high (test results weird)

CH -- 180

NaCl -- 1200

A cheap test strip showed similarly high ph and chlorine.

Temperature is 103 (heater working fine).  And the SmarterSpa chlorine generator has power.

I've generally tried to use the Dichlor/Bleach method and Nitro's approach to water maintenance except I've had a SmarterSpa chlorine generator for the last couple years.  I get the chlorine level up with dichlor but then use the smarterspa to keep chlorine steady (knowing I'm lazy).  It's worked great, save for once when the transformer went out on the smarterspa and chlorine dropped to zero for an extended time without realizing it.  Ahhsome, sanitize, water change. Generally the water parameters remain stable and I don't do much beyond change the water every 9-12 months. I've gotten even lazier because of that historical stability and my wife will let me know there's something off with the water.

Last water change and balancing was early October, five months ago.  I confess I've neither tested nor dosed anything recently.

Certainly it needs a cleaning and a water change, but I'd like to figure out what happened and how damaged the components are. Is this residue some sort of degraded metal?  It's an enclosed backyard; I doubt it was vandalism.  If the chlorine had been sky high a week or so ago when last used, my wife would have complained.  It's like something gave out quickly, or someone dropped a piece of metal in the tub.

[NathanielT]

Bump?

[waterbear]

Your chlorine is extremely high. You cannot measure pH or TA when the sanitizer is high. Period.

https://www.poolspaforum.com/forum/index.php?/topic/58991-false-high-ph-readings-when-shocking-some-truths/

On 2/10/2025 at 4:47 PM, NathanielT said:

I get the chlorine level up with dichlor but then use the smarterspa to keep chlorine steady (knowing I'm lazy).  It's worked great, save for once when the transformer went out on the smarterspa and chlorine dropped to zero for an extended time without realizing it. 

This tell me that you aren't testing your chlorine on any type of regular basis. You need to test at least weekly. This is also probably why your chlorine went through the roof.  There is nothing wrong with using your SWCG to maintain your chlorine in the spa BUT YOU NEED TO STILL TEST YOUR WATER ON A REGULAR BASIS!

 

On 2/10/2025 at 4:47 PM, NathanielT said:

Generally the water parameters remain stable and I don't do much beyond change the water every 9-12 months. 

Water should be changed in a spa every 3 to 4 months because of the high bather load to water ratio! Without testing you have no idea how stable your water parameters are.

On 2/10/2025 at 4:47 PM, NathanielT said:

I've gotten even lazier because of that historical stability and my wife will let me know there's something off with the water.

And there is your problem! We can give advice but we can't fix lazy. Without testihg how would your wife know that the water is not OK.

On 2/10/2025 at 4:47 PM, NathanielT said:

confess I've neither tested nor dosed anything recently.

And you wonder why you are having problems? Really?

On 2/10/2025 at 4:47 PM, NathanielT said:

but I'd like to figure out what happened and how damaged the components are. Is this residue some sort of degraded metal? 

What happened is that you ignored the spa for an extended period. The residue is most likely filter endcaps and/or other plastic parts that have degraded but it also could be oxidation of metal parts in the heater and/or pump seals. No way of knowing from the picture.

On 2/10/2025 at 4:47 PM, NathanielT said:

If the chlorine had been sky high a week or so ago when last used, my wife would have complained.

How woiuld she know? IF the FC is high and you have CYA in the water (from your use of dichlor) then, depending on the CYA reading, the FC could be very high and you might not know. You can't really smell FC, you smell CC.

On 2/10/2025 at 4:47 PM, NathanielT said:

It's like something gave out quickly, or someone dropped a piece of metal in the tub.

It seems the water has a clear greenish cast. That is often an indication of copper. Black staining that does not wipe off can also be an indication of copper. Heater are often a source of copper. Was your SWCG an add on and is your heater designed for a salt spa?

Both salt and high sanitizer or a very low pH can causer copper to leach into the water and destroy the copper parts.

 

[waterbear]

Moving this thread to the hot tub water chemistry section of the forum.

[waterbear]

On 2/10/2025 at 4:47 PM, NathanielT said:

It seems to come off with a magic eraser, albeit not easily. 

DO NOT use a magic eraser on the spa. It is a melamine foam  abrasive cleaner that can damage the spa surface. This is why they do not recommend its use on acrylic bathroom fixtures such as sinks and bathtubs.