Weird shiny black deposit from pool heater drain plug?

[m_hurley]

Hello,

I have a strange problem. As part of winterizing our pool this year, we removed the drain plug from the pool heater and disconnected the outlet pipe on the side (to blow water out of the pipes into the pool). After a month or so, I noticed this black deposit dripping out of the drain and disconnected pipe. It would then harden on the floor. The deposit is shiny and metallic, and near odorless. I thought maybe it was manganese, since I've read that can stain pools black. But this stains my fingers yellow, instead of red or purple. It reminds me of the black metallic deposit formed on our washing machines when bleach reacted with the chrome finish.

Here are some pictures:







As you can see in some of the pictures, it looks like there is some rust when it dries or hardens. We have had problems with our previous heaters getting corroded and needing to be replaced after a few years. I think this was largely due to poorly balanced (corrosive) water. However, this current heater is 5 1/2 months old, and I wouldn't expect anything like this so soon.

My only two ideas as to what may have caused this are as follows:

1) We used bromine until July 8, and then switched to chlorine (two weeks after replacing the heater). We replaced the tablet feeder so we wouldn't have a chemical reaction there, but the pool heater may have been corroded by traces amounts bromine reacting with the chlorine?

2) A little over a month ago, the pump stopped circulating overnight, presumably because of a clog somewhere. The pump and the pipes around it were super-heated because the water had backed up and wasn't going into the pool. The pump was making a strenuous sound, and the water in it was bubbling hot. I shut it off and took the pipes apart, ran a snake through what I could, and took the pump apart to check the impeller. After fixing pipe leaks (some of the sealant had melted), I turned it back on and everything worked normally. NOTE: our inline chlorine feeder is installed between the heater and pool, so super-chlorinated water doesn't pass through it. But in the period when the water was backed up, some super-heated, super-chlorinated water from the inline feeder may have circulated back into the heater, corroding things?

As I said earlier, the pool has been pretty well balanced since the new heater went in. And in fact, the chlorine feeder has trouble just keeping the pool up to acceptable sanitizer levels, so the heater would never really have been exposed to very chlorinated water (except possibly once as described above). The pH was never low for more than a couple days at a time. The only other thing is that we built up REALLY high CYA levels before I thought to check them (still learning things about pool chemistry). But I don't know if that can corrode metal heater parts.

Any ideas on what this black substance might be, and what caused it? Thanks in advance for your input!

Matthew

[PoolDoc]

I edited your pictures some, before posting them.

I can make out the location of the first picture, but what are we seeing in the next 3? I gather that #3 & #4 may be the deposits on the floor, but what is #2?

In any case, I don't have any immediate answers; just more questions. Bromine does not, so far as I know, produce any compounds like that, and I've not *ever* seen green goo of that color in a heater or pump. (Bluish-green would suggest copper.) So, here are the questions:

1. Make / model of heater?
2. Specifically, what winterizing chemicals were used, and where were they added?
3. Has *anything* other than pool water been in the heater?
4. Can you provide some 'overall' context pictures? (Often some relevant is not mentioned, but will show up in 'wide shots'. In particular, make sure the feeder's location on the piping, and relationship to other equip is clear.)
5. What are current test results on your pool, and how are you testing?
6. What is the water source for your pool (well / city / tanker / etc.)
6. The stuff in picture #2 looks bubbly and green in the picture; is that correct?

[PoolDoc]

. . . membership updated.