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So there is +/- 0.5 ppm for the 10 ml sample size it looks you are using, but it's clearly using up more chlorine initially at around 2 ppm FC dropping to 1 ppm or less at the end. The 2.5 ppm between Thursday and Friday is a blip but may really be 2 ppm and perhaps was a sunnier day. I...

That's not usual. Usually during the day one loses more chlorine at higher FC levels, CYA held constant. The loss is roughly a percentage loss. This is why the daytime losses when doing a SLAM are much higher than at normal FC/CYA levels. For your 19 to 4 in a week (which by the way would be...

Full-strength Muriatic Acid (31.45% Hydrochloric Acid) has a high vapor pressure at higher temperatures. This paper and page 2-76 in this paper show that the vapor pressure of the acid at 40ºC (104ºF) is about 81 mm Hg or about one-tenth of an atmosphere pressure. Water vapor pressure adds...

There's a pool service called PoolChlor that does this (or used to do this) where for some pools they use a combination of chlorine gas and chlorinating liquid (but for chlorine gas you need special permits). 14 ppm FC with 100 ppm CYA has an active chlorine level of roughly 0.14 ppm FC and is...

The reason for the higher CYA target for SWCG pools is not just that it saves money by losing less chlorine to sunlight, but the lower SWCG % ontime means that the rate of pH rise should be slower as well. So it's not just the saved money from lower electricity cost or even from using less...

So if the TA settles to some amount where acid addition isn't lowering it, then that means that either the amount of TA being added from evaporation and refill is matching that lowered from the acid addition or that the pH rise is not from carbon dioxide outgassing (or a combination of these two...

Most of the pH rise in pools either using a hypochlorite source of chlorine or using a saltwater chlorine generator is from carbon dioxide outgassing because the TA is set too high or the pH too low. Try lowering the TA to 70 ppm and target 7.7 as your pH and see if things improve.

You can always use rain overflow to dilute your water and keep CYA in check. And you can always raise your FC target if your CYA level is higher. There are no absolutes such as never using Trichlor. You just need to understand and deal with the consequences. Some pools with short seasons and...

For one week, using Trichlor pucks and possibly raising the FC level usually works well. For two weeks, that is harder but if one has an inline chlorinator of sufficient capacity and sets its output appropriately then they might be able to get by with 2 weeks. The CYA level may rise more over...

The active chlorine level when the FC is at SLAM level which is about 40% of the CYA level is the same as in a pool with an FC of 0.6 ppm with no CYA so less than found in commercial/public pools. Nevertheless, as my wife can attest to after swimming in an indoor community center pool every...

If you reverse the equilibrium equation Matt showed: HCO3-- + H+ ---> CO2(g) + H2O Bicarbonate Ion + Hydrogen Ion ---> Carbon Dioxide Gas + Water you can see that the hydrogen does not leave the water but rather goes from being a separate ion to being part of a water molecule itself. You can...

Previous posts said that DE was added to the filter, but I think James is right that at high speed with a 1.5 HP pump it was blowing debris through the sand filter too much. The more recent clearing may be the combination of running at the slower speed combined with use of DE in the filter. It...

Saltwater chlorine generators are VERY common in Australia and as was suggested by Matt (JoyfulNoise) above, that may be a very reasonable option for ease of maintenance. Of course, there is up-front cost, but ongoing cost can be low. If you use any technique that doesn't maintain a...

See the relative kill times for chlorine vs. copper and silver in the table in this post. Copper is an algaecide, but does not kill fecal bacteria and metal ions aren't great at inactivating viruses. So while you may not get visible algae, that doesn't mean your pool is safe from pathogens...

The philosophy at TFP is that if you properly maintain your pool's FC/CYA ratio on a consistent basis, then you should not need to elevate the chlorine levels on a regular schedule -- that is, you should not need to "shock" your pool in the pool industry sense. Part of the reason for the pool...

Unless they are using a lot of algaecide, you could throw some (mostly phosphate) fertilizer in that pool and see the algae develop. The other thing that can happen is when the bather load is high enough to have a lot of monochloramine in the pool (that shows up as CC) since that kills algae...

Glad you were able to easily resolve this issue. Drops should come out well-formed and without difficulty from most bottles. The only ones that are harder are the smaller 0.5 ounce bottles for the R-0010 and R-0011L in the TFTestkits TF-100 because being smaller bottles they are harder to...

Clorox Germicidal Bleach does not have additives that are a problem for the pool. It's "splash-less" and "outdoor" bleaches that have more excess lye and/or thickeners in them that you don't want added to the pool because they can cause foaming and excessive pH rise.

Welcome to TFP! :wave: For a week you could use Trichlor tabs in a floating feeder. For longer than that you'd need a higher capacity inline chlorinator. Or you can have a neighbor or friend come over twice a week to add chlorine if you use a pool cover.

If you look at the Recommended Levels for a plaster SWCG pool you'll see that your pH and CH are both low. You say you normally have the pH at 7.5 but usually in an SWCG pool the pH will tend to rise and it will do so faster when the pH is lower which is why we normally recommend 7.6 to 7.8...

If you're doing the test with the FC as high as 30 ppm, then I'd lower the FC to 20 ppm and redo it. There's a percentage testing error that can have you fail the test though usually you'd get inconsistent results each time you do it. At 20 ppm FC you should get better accuracy and hopefully...

That is normal and not a problem. A higher TA or a lower pH causes more carbon dioxide outgassing and that has the pH rise faster. Stop trying to lower the pH so much, certainly not below 7.5. If it's fairly stable at 7.8, then leave it there. If your TA or CH are high and you are worried...

Yes that is helpful since in the U.S. we are used to 8.25% bleach vs. 10% or 12.5% chlorinating liquid so they are more comparable and are priced such that one may be cheaper in one area while another is cheaper in another area. Your 4% bleach is more like our off-brand inexpensive bleaches...

There are over 400,000 visitors per month to this site during May, June, and July each year so the increased use of the least expensive reasonable quality chlorine products is not surprising.

The Liquidator is different since it relies on keeping the chlorine and water mostly separate. The chlorine is added from the bottom and sits on the bottom while water flows over it above it. Diffusion and some mild water flow mixes some chlorine in to the water above and that gets pumped into...

Of course, both statements are true -- Mark (mas985) summarized it well. Chemicals that dissolve in water and are mixed with water will stay mixed in the water and not separate (with some unusual exceptions I describe later). The only reason The Liquidator works with the chlorine on the bottom...

They use Trichlor tablets/pucks because they aren't visiting the pool more than once a week so need to provide chlorine dosing when they are not there. The tablets/pucks are convenient, but insidious, because for every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid...

So the bottom line is that if you are able to consistently maintain the FC level, then they are close to the same at preventing algae growth (8 ppm FC with 60 ppm CYA would be almost exactly the same) and everything else associated with the active chlorine level such as the rate of oxidation of...

For a larger commercial/public pool especially with higher bather load, you need high-capacity feeders (unless you go with commercial SWGs) and there are companies that specialize in these and other systems for such pools (e.g. Treatment Specialties and their High Capacity Feed Chlorination...

No, outgassing doesn't affect calcium or copper at all. They are completely unrelated. Dissolved solids and metals do not outgas. Volatile gasses outgas such as carbon dioxide if it is over-saturated in the water (which it is) and some volatile organic compounds can outgas (such as some...