What's up with muriatic acid?

Jump to latest Follow Reply
I thought I'd talk a bit about the results of all this.

First, there hasn't been any change to Muriatic Acid (HCl), except that the concentration has dropped in the stores. We used to be able to buy >30% mixes anywhere we went, but now the big box stores carry stuff that is less than 15%. In my location, Leslie's and Ace Hardware carry 29%. Calcium Carbonate will react just fine when hit with the 15%, and even more so with the 29%, but Calcium Sulfate won't. Note that Calcium Sulfate will dissolve in HCl, but it takes longer and doesn't boil, so you may not know it is happening. That's why one should leave a chlorine generator in the acid bath for some length of time to actually get the stuff off. Personally, I seldom use an acid bath on the chlorine generator; I use a lower power power washer (1200-1400 psi) to clean the thing because I can't help but think the acid wash will shorten the life of that expensive part. The power washer also does a pretty good job on the cartridge filter elements I have if I'm careful not to blow a hole in them (you only make that mistake once).

I couldn't find a way to get the Ca out of the pool chemically. That left changing the water, but my CH of the available water didn't seem to make that a good solution. I'd just be back in the same situation in a short time. I've been told, but haven't proven it yet that peak evaporation in my area can reach 300 gal/day. Now, I have no data on how big a pool that is, how deep it is or how warm the person kept the pool, so that is just rumor. However, the evaporation rate is high in the summer; it gets to 135F in the sun (yes, I measured it) at times here so evaporation has to be high. Remember, the temperature in the sun is considerably higher than the air temperature. So I had a reverse osmosis machine come out and treat the water. My loss was in excess of 2000 gallons from a 10,000 gallon pool, but that was because the water was so high in CH that it took a lot to purge the membrane in the filter. As the process progressed there was a visible decrease in the waste water produced so it was obvious that things were getting better as the water was cleaned up.

I had the guy (over his objections) take the pool down as far as we could get it. My measured CH was around 150 and the guy told me that that would cause problems. My pool is pebble tek and tile with totally plastic fittings everywhere. I wasn't worried except where the tile grout was exposed at the top of the pool. This turned out to be a wise decision because it softened and eventually dissolved the calcium line at the waterline of the pool. Yes, I noticed it was getting soft and hit it with the power washer to force a lot of it off, then raised the water level to cover the remaining line. Over a couple of days it softened it as well and a little scraping with a stainless steel putty knife got 95% of the rest. I'm still waiting for the tiny bit remaining to dissolve and then I'll take the water level back down. I'm sure this line will come back over time, but I know how to fix it now. Yes, my CH level is still low, but I expect the desert water and dryness to take care of that problem for me; most likely sooner than I want. So I saved a considerable amount of work scraping or money having the pool blasted with those little glass beads to clean off the calcium line.

This episode probably cost me around $600 or a little over that to complete, so weigh the factors carefully making your own decisions how to proceed.

And, have fun.
 
draythomp said:
I've been told, but haven't proven it yet that peak evaporation in my area can reach 300 gal/day. Now, I have no data on how big a pool that is, how deep it is or how warm the person kept the pool, so that is just rumor. However, the evaporation rate is high in the summer; it gets to 135F in the sun (yes, I measured it) at times here so evaporation has to be high. Remember, the temperature in the sun is considerably higher than the air temperature.
Click to expand...
You can see from this map that pan evaporation rates for Arizona range from 80-120" per year. In a pool with 16'x32' surface area and assuming 120/365 = 0.33" per day, that would be 105 gallons. Even if the rate were double in the summer, that would be around 200 gallons per day. The 300 gallon/day may be for larger pools or in windy areas. As for temperature, you always measure air temperature in the shade since measuring temperature in the sun depends on the reflectivity of your measuring device. A darker device will absorb sunlight and heat up and if not highly conductive to the air it can build up to very high temperatures (think greenhouse effect). The pan evaporation rates are averages and take into account average temperatures day and night. So the peak during some parts of the year can be higher.

Wind is a HUGE factor in evaporation rates so if you are in an area that is windy and the pool is not sheltered, then that can significantly increase such rates. During July (and pretty similar in August) in Phoenix, monthly average daytime high temperature is 102ºF while nighttime low temp is 76ºF for a rough average (biased upward) of around 90ºF. The relative humidity ranges from 43% in the morning to 20% in the afternoon. If I assume a water temperature of 90ºF, relative humidity of 20%, air temp of 102ºF, then the evaporation rate with no wind is 0.31" per 24 hours during the day (it's 0.32" per 24 hours at night with higher humidity but lower air temp). With just a 2 MPH wind, this increases to 0.60" while with a 5 MPH wind this increases to 1.02" per day. The wind is measured near the surface of the water (average wind speed in Phoenix during July is 7.1 MPH, but will be lower at the pool's surface). The sun does not directly evaporate water -- what it does do is heat the water to a higher temperature and it is that higher temperature of water that has the evaporation be faster. This is why the evaporation rate stays pretty constant day and night (the exception is during times of year when there is a lot of dew as that causes the air to have less water content during early morning).
 
A good thing about the RO treatment is that it also reduced any sulfates, which along with the lower calcium hardness will help reduce the formation scale. There are several commercial products designed to remove calcium sulfate scale, such as Dow Versene.

Overall, it sounds like a reasonably good outcome. I think that a water softener should be able to help manage calcium buildup in the future.

I would recommend that you avoid any products that contain sulfates, such as sodium bisulfate or Potassium peroxymonosulfate.
 
chem geek, you're not wrong, but may be giving the wrong impression. No, the sun doesn't evaporate the water, but the sun heats the water that causes evaporation. Similarly, the burner on my stove doesn't evaporate the water, it heats the water so it can evaporate. What actually happens here (contrary to the scientists that don't actually care for a pool in this climate) is that the ground temperature, even 5 feet under the surface is at 90F and the sun beats down directly on most pools. A basic glass mercury thermometer placed directly in the sun will hit 180F. Glass, reflective mercury 180?? If you shade it, like an umbrella over it, it will still hit 135 from reflective energy. Cool deck will burn your feet until you splash some water on it. You can't sit on the side of the pool long, it will burn you. There's no such thing as a cold water tap, it's at best tepid, sometimes warm. The water in the pool is cooler than the air and draws the air which carries away the evaporant so the pool is constantly evaporating water away due to the almost undetectable, but present, breeze. A wind will truly accelerate this process by hitting the water with a very dry material to absorb even more water and carry it away. Like taking a sponge to a dog bowl. Patios work because of the size, larger area under the shade and it can actually cool off to a tolerable (well, for people that live here) level. We still use misters for flash evaporation effects; at least until the calcium clogs the orifice.

In this climate, they talk a lot about dew point, because we never reach it. I haven't seen dew on the ground in, what, six years? And, that was the day after a winter rain. We have rain that falls from the clouds and doesn't reach the ground. That happened last week and raised the humidity up to almost 40%. Yes, there is the occasional snowfall, lasts about 20 minutes or so. The ground is so dry that you can't water it, it just runs off unless you gently soak it for hours and hours. This is the area where they mine the stone that makes those cool coasters that absorb the water from cold drinks that leave the table dry. The weather professionals put their devices in odd places where the readings are jaded. I have never seen the humidity get to 40% at night unless it was just after a rain. 5-15% is more like it. The women here bathe in Eucerin dry skin treatment and every car has a stain on the upholstery from the tube of Chap Lip that melted into it. This is the place where the dust storms make national news because they rise MILES into the atmosphere and literally encompass mountains in their path. One of two places in the the world this happens. http://news.yahoo.com/photos/dust-storm ... slideshow/

For example, get a glass of water, put it in the sun and it will be gone in an afternoon. Sometimes, before the afternoon finishes. This is how I tested the precipitant from evaporation for solids. A glass of water is clear, secluded from the wind, reflective, and yet, hot. I don't question the methodology of pan evaporation rates, but their applicability to pools is only as a comparison to other areas. Pools are large enough to create their own little environment with breezes, bugs and freaking calcium concentrates.

It truly is a dry heat.
 
draythomp said:
No, the sun doesn't evaporate the water, but the sun heats the water that causes evaporation.
:
A basic glass mercury thermometer placed directly in the sun will hit 180F. Glass, reflective mercury 180?? If you shade it, like an umbrella over it, it will still hit 135 from reflective energy.
:
In this climate, they talk a lot about dew point, because we never reach it. I haven't seen dew on the ground in, what, six years?
:
For example, get a glass of water, put it in the sun and it will be gone in an afternoon. Sometimes, before the afternoon finishes. This is how I tested the precipitant from evaporation for solids.
Click to expand...
If you circulate the water during the day, especially near the surface, then the pool surface isn't going to get so hot as to significantly affect the evaporation rate. However, if the circulation near the surface is poor then to the degree that the surface water is hotter, the evaporation rate will be faster. If the pool surface were 100ºF instead of 90ºF, then the rate goes from 0.31" to 0.47" while if it were 110ºF then the rate goes to 0.68". The thing is that while 24% of the sun's energy is absorbed in the first inch of water (see this post), evaporation cools the water. So if you find that the water surface is much hotter than depths, then if you were to improve surface circulation you would reduce evaporation.

Mercury is not a perfect mirror and it is dark enough to absorb significant sunlight. Even more important is that it is in glass which passes light through but reflects infrared and insulates so causes the mercury to build up temperature. Putting a thermometer in the sun is not a valid way to measure air temperature. As for temperature in the shade being hotter because of radiant heat from the ground, that is of course perfectly valid and would be captured by standard temperature measuring instruments. So while some days may be exceptionally hot, how is it that the average daily high for Phoenix is 102ºF (see this link)?

When I wrote about dew, I didn't mean in Phoneix and I should have been more clear about that. I meant more generally since in areas that do get dew in the winter the water content in the air changes (gets lower in the early morning -- relative humidity is 100% which is why dew forms, but the temperature is cold so absolute water content is low). As you point out, the relative humidity in Phoenix (see this link) doesn't normally get to 100% at any time of year.

It would be an interesting experiment to take a glass of water during the day on a white styrofoam surface (so as not to heat the water by more than what would occur in a white plaster pool -- not on a colored cement surface that will get exceptionally hot) and note how quickly it evaporates. Then repeat the experiment at night. The pan evaporation rates are determined by methods described in this link -- note that the pan is raised somewhat above the ground. A tall glass is not a broad pan, but I'm surprised by the huge difference in evaporation rates between what you see with a glass of water vs. what is seen by weather service pan evaporation. Did you ever do a bucket test to measure the evaporation rate as described in Leak Detection?
 
good point about temperature difference depending on depth. I actually don't know. Getting into the pool stirs it up enough around the body it all seems the same. Unfortunately, it's getting into fall so I can't test it in a really hot situation. I actually have a foot or so of shade on the pool now due to the sun dropping behind the house . I can try it a little bit and see if there is a significant difference though. May be able to tell something.

Regarding average daily temperature, I don't have a clue why their records differ from experience. For example, when I stop at a stop light on a motorcycle, my handlebar thermometer says 110, the news reports 101 for the same time. Sure there's blacktop and a hot motor under me, but when I take off and the wind is 45 mph, it still says 110. At that point I pull into a shady place and set there for a while. If I take off on little streets going 60, it still says 110, then I go past an alfalfa or corn field and down it drops to 90 or so; feels real good. I've seen the temperature in the shade on the patio at 115 and news reports 104. In town, they constantly complain about the difference between reported temperatures and what is measured at their house. Same on the other end. Last winter, an exceptionally cold one, my lowest was 15F, the town thermometer got down to 20. I think the little louvered houses they put those things in shelter the devices such that, though consistent, are not what the people experience. However, on the day where it got down to 15 at night, it warmed up to 60 during the afternoon; the sun really cranks it out here.

Humidity is different. My instrumentation isn't good enough to argue with the charts except for the averages in the winter. It doesn't get that high for an average in December. At least not out of town. Of course, out here there are no lawn, parks, golf courses or fake lakes to affect the readings. I would bet 40 or so is where it really is, but I have nothing reliable to base that on. My neighbor has a good meter, but he hasn't been here for a winter yet. We'll see over time.

When I evaporated the glasses of water, I wanted the water gone because I was looking for the residue. I sat the glass on a light brown cinder block retaining wall. It would have been about the same as setting it on the ground because the dirt is roughly the same color as the block (intentional). The temperature today got up to 107 in the shade, so I can probably try the styrofoam trick tomorrow. I suspect it will evaporate more slowly, but it's still 6 inches of water in an enclosed transparent container that doesn't have the surface area to allow evaporation. There is the heat transmitted from the surface through the glass that could be a major factor. Don't know. The folks here put their horse troughs in the shade though to limit evaporation and heat gathered by the tubs. These things are pretty large and at least 18 inches deep, the calcium line in them is usually about two inches wide showing how low it got before they refilled them. Not a good measurement though since different people refill on different schedules.

An interesting item on the temperature chart is the record high. That must be the record high average temp because there were many, many days this year where the temperature was well over the 114 they show on the chart. Last year we had 6 days in a row over 120 as measured in town. The news here went nuts with heat warnings and lectures about hydration. So, 114 absolutely has to be the average. I personally haven't seen an entire month that would average out at 113, that would be murder. I have seen the temperature get to 126 at the freeway rest stops. This is in the shade with one of those state calibrated temperature gauges, so I think it was probably really close to correct. Yes, we have coolers for the bathrooms here at the rest stops.

But, getting back to swimming pools; it seems a hundred gallon evaporation rate is not totally out of line and would explain how my Ca level got so darn high. One of the folk that services pools said that the CH could go up around 40 per month. Again, I have no evidence for that, but it doesn't seem totally out of line if the evaporation rate is at 300 for big pools. So my evaporation rate could raise it by half that. Especially if I run the waterfall and fountain to cool the water off.

Just for fun, here is a chart of today's temperatures by the minute (mostly):

Untitled.jpg


The blue line is temperature and the red one is my instantaneous power usage. Yes, I get to that level of detail and store it for analysis. The reason for the rapid increase at the beginning of the day is because the sun hits the temperature sensor and then rises enough so it's in the shade for the rest of the day. I captured this image a couple of moments ago so it is mostly up to date. If I were to compare this to the weather report, there would be a world of difference. And, yes I measure the pool also, but only when the pump is on. The sensor is in the plumbing so I can only get a reading when water flows. Otherwise it reads whatever temperature the pipe gets up to and that is way above what the pool is.

And, yes Tucson is even dryer than here. Those folks get it really bad. The dirt storms start there too. I don't know about the temperature though, never checked.
 
Thanks for the info. The government weather sensors may not be in areas with a lot of radiant heat (i.e. not in the city with asphalt) though I wouldn't consider that to be a fair estimate for a city. If you look at Weather Underground for the sensor at KPHK (which seems to measure higher temperatures), you can see some higher average highs in July of 105-106ºF and you can see the record high as well. In that chart, the data is daily so the (maximum) highs are noisy while the average (over years) is smoother.

For a tall clear glass, the extra surface area letting light into the glass on the side and absorbed by the water may be a factor, especially that more water is "near the surface" of heating by the sun. The temperature of the water might be getting much higher. You could measure the temperature of the water in the glass near the surface when its evaporating in the sun to find out. As for the smaller surface area for evaporation, it's all proportional so the height of water that is lost so should be similar were it not for the temperature difference. It is true, though, that the sides of the glass would tend to limit the wind effect (it still has an effect, but less so).
 
I know the original topic wasn't thermometers, but it is now :)

When a thermometer is inconvenient to get to, make one up...

"During the renovation, rangers stopped making the afternoon check at the weather station. Instead of listing N/A, or not available, for Death Valley, AccuWeather listed a ballpark figure, set arbitrarily as one degree below the state high."

"...they were estimates that were often way off — by as much as 15 degrees either way."



http://www.signonsandiego.com/news/2011 ... abricated/
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply