Muratic acid safety

[chem geek]

Isn't the acid strong enough that by the time you finish pouring, then grab the brush and brush it. That it has already had a chance to sit on the bottom and do damage?
Does this apply to vinyl liner pools as well?

If the acid doesn't get mixed because it misses the return flow and sinks to the bottom since it is denser than water (until it gets diluted), then this pooled acid on the bottom can be a problem if it stays there for too long. Brushing soon after addition should disperse, mix and dilute it before it becomes a problem. If not brushed and if pooled, then it could sit there for an hour or more and over many applications like this it can cause damage by dissolving some of the calcium carbonate in plaster.

Vinyl pools would also be a problem since acid is the worst thing for vinyl. In fact, it's probably even more important to do the brushing in a vinyl pool than a plaster one since the resulting damage to vinyl is far worse. For plaster, it's just etching away a part of the surface, but for vinyl you're talking about a complete failure (i.e. thinning and breakage).

 

[RobbieH]

Maybe I don't see issues because the four returns at the shallow end of my pool are so powerful and so close to each other. My pool turns over pretty quickly, I don't ever see the acid pooling around the returns for any length of time. I do see it as it's going in, but it disperses quickly.

I bet my attitude changes though when I have a perfect surface.

 

[y_not]

For purposes of seeing where it settles, or if it does. Can we put food coloring, or some other type of dye in it that'll break down later?

I'm not thinking every time, but more like 1x to see where it flows and if it gets mixed up enough.

Is it heavier than say 8.25% bleach?
I ask because I can see that when I pour it in, it's kinda shiny, but not rainbow colored like antifreeze on water. It swirls around the corner, sinks about 1/2 way or more, then just disperses into a feather of a wisp that I can no longer see. It's probably not totally gone, IE maybe some concentrated clusters remain. But it just dissipates so much that I can't see it anymore, at least at the angle I'm at in front of the return.

 

[chem geek]

Look at this link for how acid will pool if the circulation isn't good. See Graph C for the acid puddle. That was done with the pump off, but is the type of problem that we're trying to avoid if the acid misses the return flow and settles to the bottom without getting drawn into the main drain. Though you could use dye for a test, you probably wouldn't want to add 2 cups the way you would for acid and if you added only a small amount then that wouldn't be a viable test.

As for density, full strength Muriatic Acid (31.45% Hydrochloric Acid) has a density of 1.16 g/ml which is about the same density as 12.5% chlorinating liquid. 6% bleach has a smaller density of around 1.08 g/ml. Anything denser than water will sink, though the denser it is the faster it will sink. If it mixes and gets diluted before reaching the bottom, then it will stay mixed so won't be an issue.