Dishwashing (pan) Detergent Decomposition?

Factual Questions
1

OK, have pool, OD’d it on CYA (now 100 ppm; s/b 40-50 ppm).
There is a chemical reaction (anaerobic, IIRC) whereby this will decompose.
The usual fix would be to drain 7,000 gallons and refill. With the drought, that isn’t going to happen.
I decided to pour mineral oil on the surface (to exclude oxygen).
I got patches where the oil did not cover, hence the detergent.
It spread and displaced the oil.

Q: will the detergent decompose and allow the oil to spread, or should I just give it up. drain the water and let the rain (if any) re-fill?
Or am I just screwed?

2

Oh, dude. A little knowledge is a dangerous thing.

Certain bacteria will, indeed, decompose cyanuric acid under anaerobic conditions; I don’t think you want to encourage that sort of thing in your pool.

There is a chemical pathway to degrading CYA; it’s normally regarded as a problem, so it’s unlikely to have been studied as a deliberate technique; it requires higher temperatures, so it’s unlikely to occur in the winter; and it would take years to lower your CYA levels significantly.

It would take many, many gallons of mineral oil to create a stable boundary layer on the surface of a swimming pool, and you’d have to drain to get rid of it. As you’ve discovered, water excludes oil by minimizing the size of the boundary, which gets you huge blobs, not a thin film.

Detergent will not make oil spread out across the surface of the pool, it will solubilize or sequester it, depending on the ratios involved. A significant part of your pool is now, essentially, skin lotion. Cheap, nasty skin lotion (or - depending on how much detergent you added - cheap, nasty conditioning shampoo).

All you’ve done is contaminate your pool, and I can’t begin to guess how it’s going to affect your filters and whatnot. Yeah, draining. More than if you’d just left it be, I expect. Though I respect your determination to avoid wasting water (California? Me too), you and the environment would have been better off if you had, say, come here first.

Moral: Tri-Chlor tabs are bad, m’kay?

3

I didn’t use tri-chlor - I did the OD the hard way - about 8 lbs CYA in a 15K gallon pool.
Actually, I got the rid of last year’s CYA (when I didn’t want to) - including the oil (no detergent at that time).
I have a cartridge filter, so I can get rid of the floating crud - it is is still there come June.
I was simply trying to duplicate the conditions of last winter, and hoping the same reaction would occur.
The theory was that I somehow got the CYA to produce ammonia.

One of the folks at TFP wants a sample (anaerobic, of course) should I get this to happen again - it seems he has an ongoing debate with another chem expert as to whether or not a residential pool could produce the reaction.

Last year, I went from 50 ppm CYA to 0 (in the CA central valley). Couldn’t figure out why I was losing FC in large quantities. 0 CYA does that.

Would good old TSP clean the carts, should I manage to colllect the assorted curd onto them, or should I just too the carts?

4

Oh - the oil is actually 15 year old aircraft engine oil - who knows what all is in it - but it did make for a nice even sheen (except for the spots which got detergent).

5

You put aircraft engine oil in your pool? :confused: :dubious: Even if it did work, how did you you intend to deal with your now-oily pool?

6

As stated, the oil is actually mineral oil - a/c engines run too hot for petroleum (ever hear of Castoil? Castor Oil was used in some WWI - era planes).
If the sunlight does not destroy the oil, the filter cartridges will remove it.
In the meantime, no more mosquitoes.
And the detergent seems to be breaking down faster than the oil - the sheen is returning.

7

I sense this will be one of the great straight dope screw ups remembered for years.

Right up there with washing the couch cushion covers.

8

Mineral oils are still refined petroleum. Either way, interesting that you thought the sun and pool filters were going to take care of that :smiley: Do keep us in the loop!