Say No to Liquid Chlorine and Muriatic Acid

Let’s talk Salts and Acids, Blisters and Stains…

People ask why we don’t like Liquid Chlorine or Liquid Muriatic acid in our pools; not just like it, but state it voids the warranty.  These two chemicals are what some pool service companies use for sanitation when a chlorine tab feeder or salt system is not working properly, and they haven’t been paid to troubleshoot the issue. Or with Muriatic Acid, a cheap way to handle PH even though it’s main use is as Concrete and Brick etcher and wash due to how caustic it is opening up pores (which you don’t want to do).  The safer alternatives would cost them more per pool which individually isn’t much but they usually try to service 50 pools a week. 

Basically the Main reason: It’s how it is delivered (usually the fast pool service upends jugs of Acid and Chorine Bleach directly in the pool, and many times same favorite location. The good pool service will instead use a 5 gallon bucket, fill it with pool water, dilute with liquid chlorine or liquid acid then slowly pour in front of a pool return). What happens when the service then fails to keep the pool PH 7.2 – 7.6 because they are not there every day to verify the PH level is in the healthy range? The concentrated liquid chlorine (or other type of salts. Yes Chlorine is a type of salt) collect in the pores of the gelcoat and fester and convert into oxygen molecules creating bumps. 

Here you see why fiberglass boats get bumps even with an epoxy anti-foul paint barrier coat.  Salt water finds a pore in gelcoat that is not covered by epoxy (epoxy has no or few pores) and ocean water has a PH of 8-8.4 and around some areas can be as high as 9.  This shouldn’t happen with pools as with proper maintenance PH should be around 7.5. 

The big No-No, more important than type of sanitizer and PH control, is when PH rises above 7.8. High PH is the catalyst that converts salts like chlorine into pressure bumps.  If you make sure your PH never goes above 7.8, your sanitizer and how you control PH doesn’t matter as much.  During dry season, it’s very easy to see high PH.   

This is where we see pool cleaners say the manufacturer doesn’t know what they are talking about. Like when a mechanic says ignore the car manufacturer’s oil weight recommendation and instead use 10w-30.  It worked a few times for them, and the mechanic then makes it the default. 

What should you do? This is too complex!  Well basically make sure you have a properly set Salt System or Chlorine Tablet Feeder to handle sanitization to lower the use of undiluted liquid chlorine.   Then for PH control, only use a Dry Acid (like PH + or PH – in a bag sold at Walmart) which is a different chemical from Muriatic Acid and since granular, it dissolves slower and most pool service know to pre-dilute it in a bucket first.  You also need to use a Metal Chelating agent to remove metal ions which can also be a catalyst (see the science of it all below if you want to be technical or argue)

As long as your PH is in the range of PH 7.2 – 7.8, chlorine at 1-2, calcium hardness 180-250, and you use a metal chelating / mineral out product weekly, it is hard to have blisters OR stains in the pool.  Lack of proper water chemistry causes all these problems and has nothing to do with the Factory. The factory does need to make sure it’s not just a simple “mold mark” or air bubble gelcoat chip, but those would be 1-2 holes or bumps.  Usually once PH hits 8.6-9 you will have dozens of osmotic blisters occur which again is a pool chemistry issue not a manufacturer defect. 

The Factory can do things (which we do) like use high grade gelcoat that is a lighter color (the darker the color the more pores in the gelcoat usually) and use Vinyl Ester which is water proof unlike Gelcoat and Resin to reduce these chances, but if the customer or pool service uses undiluted chemicals in the same spot every week for 5 years the chances of a stain (from muriatic acid opening up the gelcoat pores previously sealed because that’s what it was made to do for concrete) or blisters (liquid chlorine in bulk undiluted constantly poured in one spot will penetrate these gelcoat pores, find a void, sit and wait until PH hits 8-9 and then turn into two different molecules one being oxygen creating pressure)

You go on vacation or your pool cleaner skips a week, you might have screwed up and bumps appear.  Why? Because inexpensive pool companies just dump the jugs in the shallow end of the pool, bump PH too high or Chlorine levels too high, and these molecules travel throughout the pool and get stuck in the gelcoat pores, or between the gelcoat and fiberglass vinyl ester layer (vinyl ester layer has very few pores / holes in it.). 

Why not to use Liquid Chlorine & Muriatic Acid

1. Liquid Chlorine and Liquid Muriatic Acid are very toxic and caustic chemicals. They are dangerous and will cause severe medical issues if not handled properly. Not exactly Residential House safe for consumers to use. 
2. Undiluted (Acid to water, never water to acid) Acid or Chlorine poured on anything every week for years will cause etching to occur from the Muriatic Acid which will open up the pores in the Gelcoat, then the pool service usually follows it with a very strong concentration of liquid chlorine to the area just hit with muriatic acid. 
3. Anytime you have high PH levels AND chlorine that have found one of those pores to rest and relax, risks turning into a bump or easy place for stains to occur as the chlorine molecule changes into two different molecules one being oxygen.
4. Easier and Metered solutions exist that decrease the chance of accidents. Large chain stores sell bags of PH + and PH – that are granular powder form you can add to your skimmer basket.  If you have a salt system, make sure it is keeping your pool 1-3ppm chlorine no higher; we prefer 1 or 2ppm.  If you don’t have a salt system, use a Chlorine tablet tower / feeder they are very inexpensive and you can dial it to slowly add chlorine or trichlor sanitizer to the pool water again at a metered rate. 

What to use instead of dumping liquid Chlorine and Muriatic acid into the pool

1. Instead of Liquid Chlorine: A Salt Cell that is reviewed weekly to make sure it is generating just enough Chlorine that your free Chlorine is a 1 or 2, no higher. OR a Chlorine Tower / Feeder that uses 3″ tablets.  A 3″ Chlorine Tablet Feeder with Trichlor / Cal Hypo is a different type of sanitizer and will reduce the ability for high PH levels to cause blisters as there is no sodium hypochlorite to turn into chlorate ions and oxygen which creates that pressure bump and Trichlor already has a low PH level.  Downside is you might have to drain your pool more to get rid of higher calcium or stabilizer levels that sometimes occur with Trichlor. Reminder: on fiberglass pools calcium hardness should be 180-225ppm at 250ppm and higher time to drain the pool at the pump while adding fresh water in the shallow end. You should also keep an eye on your PH levels so that they don’t go too low, as 7.5 is the sweet spot as same PH as human tears but Trichlor is around 7.2 (so you may have to use some PH +). 
2. Instead of Muriatic Acid: Dry Acid (You will see bags of PH + or PH- at stores, Walmart will not sell Muriatic Acid for safety reasons inside the pool aisle so the PH + bag is what you will find and is granular form) is a different type of chemical used to control PH levels and is not as caustic as liquid muriatic acid. Since it is slower to dissolve, it has a better safety net due to the slower release of acid (again should be in the skimmer or on the way to the pump while dissolving) to make sure it doesn’t sit on gelcoat and “etch” it like how Muriatic Acid is used on concrete and brick. 
3. If you must use liquid chlorine or Muriatic Acid: Make sure you measure it properly to be exact on how much is needed to raise the Free Chlorine level to a 1 or 2. Then predilute it in a 5 gallon bucket until fully mixed then pour slowly in front of a pool return while the pump is on alternating pool returns. This will help it dilute and fully dissolve before moving through the equipment back into the pool.  

How to lower my risk of more osmotic blisters if I already have some

First, most major Fiberglass Pool Manufacturers use newer gelcoats and vinyl ester resins to reduce the risk of Osmotic Blisters and warranty against them for several years. So the risk is now minimal regardless of chemicals used if you have a newer Fiberglass Pool Shell.  But if you have an older pool or pool service used too much acid or liquid chlorine in one spot every week for a few years and have a few, then let’s keep you from getting more. 

The safest solution for sanitation

Trichlor 3″ Tablets in a Feeder tower is the best choice if you already have some blisters or want lease risk to stains and blisters, Still keep PH below 7.8, watch your calcium hardness levels and make sure below 250, and use Mineral out weekly!  We do love Salt Water systems as it feels better to swim and when the salt cell panel is set properly, is a slow measured release of Chlorine Gas, but remember Chlorine Gas can be harmful as soon as your PH hits 8-9+. Just keep your salt levels around 3500 if using a salt system, and if you are trying to reduce blisters this is where you want to keep your PH low around 7.2-7.5, and higher calcium around 225-250ppm. The higher calcium might cause white powder or calcium buildup, but will fill any gelcoat pores opened up with muriatic acid. 

Stains!

Always use a Metal Chelating agent like Mineral Out. Amazon has them very low cost and follow the directions on the bottle weekly.  This has a side benefit of sometimes very slowly removing calcium as well.  This is a preventive measure to keep from getting the more common stains. 

Jack’s Magic Stain ID Kit is small samples of their stain remover products you use on the stain to see which type of stain you have. 

Use of Erase Iron Stain Remover by Bioguard is helpful on any stubborn mineral stains.  We also recommend Natural Chemistry “Stain Free” product. 

White chalk on your pool steps and walls is from high calcium levels and high PH levels combined.  The best way to lower calcium hardness level is to open up the water spigot at the pump and drain water at the pump, while adding fresh water in the shallow end.  Do not leave the pool unattended to ensure the skimmer always has water in it during this process. Once calcium hardness goes to around 180, brush the walls daily and follow directions on a scale remover product like Natural Chemistry “Stain and Scale Remover”

If YOU are a Professional or Experienced

Not all pool professionals are the same, some are very good and an actual professional at what they do. For you, yes you can use liquid Chlorine and Muriatic Acid. However, understand any blisters that form or staining of any type is the product of how the water was balanced. The Factory has done everything short of using epoxy instead of gelcoat, which would then be harder to repair as epoxy doesn’t have pores due to limited/any styrene in it. 

1. Add chemicals slowly once diluted in a 5 gallon bucket directly to running pool return
2. Use a Log of every time you added chemicals to that pool, what the level was before you added the chemical and after 30 minutes right when you leave what the level was. This will give you an idea of how THIS pool reacts to X amount of both chemicals so you know how much exactly to use.  You will get this wrong though, you eventually will cause cracks in concrete pools and bumps in fiberglass pools. The real solution is have the chlorine tab feeder or salt system fixed or installed. Granular Chlorine can be used if heavy demand detected or increase the rate the feeder or salt system are set for. 
3. Remember, we are trying to keep the pool water balanced at 7.2 – 7.8ph, Chlorine 1-2, Calcium Hardness 175-250, and use Mineral Out weekly especially if in Florida which has extremely hard water in some towns. 
4. Use a metal chelating agent like Mineral Out per directions on the bottle. 

Science of it all

Sodium hypochlorite primarily decomposes through two competing reactions: a disproportionation reaction that forms chlorate ions and a separate reaction that produces oxygen gas (This is the pressure build up bump). 

Decomposition pathways 

1. Disproportionation to form chlorate and chloride: In this reaction, the hypochlorite ion is both oxidized to chlorate and reduced to chloride
   • Equation: 3𝑁𝑎𝑂𝐶𝑙(𝑎𝑞)→𝑁𝑎𝐶𝑙𝑂3(𝑎𝑞)+2𝑁𝑎𝐶𝑙(𝑎𝑞)
   • This pathway is favored by higher temperatures and higher hypochlorite concentrations. It is the basis for the industrial production of sodium chlorate.
2. Formation of oxygen and chloride: In this pathway, hypochlorite is reduced to chloride while also producing oxygen gas.
   • Equation: 2𝑁𝑎𝑂𝐶𝑙(𝑎𝑞)→2𝑁𝑎𝐶𝑙(𝑎𝑞)+𝑂2(𝑔)
   • This decomposition is accelerated by exposure to light and the presence of certain metal catalysts, such as copper, nickel, and cobalt. The buildup of oxygen gas can create pressure issues in storage containers. 

Factors influencing decomposition

• Temperature: Higher temperatures significantly increase the decomposition rate for both pathways. The chlorate-forming reaction becomes more dominant at higher temperatures.
• Concentration: More concentrated sodium hypochlorite solutions decompose faster. For a given temperature, a lower concentration is more stable. Ding Ding Ding. Your pool service just learned undiluted chlorine / bleach is harmful and they need to stop using it on all pool types including concrete pools which also have pores which will cause cracks. It’s not just Pettit Pools or AI saying this, but from the manufacturer https://hillbrothers.com/pdf/Product-Profiles/Sodium-Hypochlorite-Stability.pdf
• pH: The decomposition reactions are influenced by the pH of the solution. No lower than 7.2 and no higher than 7.8 on ph. 
• Impurities: Transition metal ions (e.g., copper and nickel) act as catalysts for the decomposition reaction that produces oxygen. Use a Metal Chelating Agent to help lower metal ions which also reduce metal stains.
• Light: Exposure to UV light speeds up the decomposition process. 

Salt cells shocks pool salt that you have added to the pool water from a bag whenever your salt cell board shows 2800ppm salt, and turns it into hypochlorous acid and ALSO sodium hypochlorite the same as Liquid Chlorine. That’s right no difference between salt cells and liquid chlorine. However, with a Salt cell we have a slow measured release of chlorine which is far safer and simpler then just dumping jugs of chlorine bleach into the pool which will land on gelcoat before it dilutes. 

Chlorine Tablets are commonly use trichlor (trichlor-s-triazinetrione), or sometimes calcium hypochlorite (cal hypo).  Using a 3″ chlorine feeder / tower with Dry Acid is the safest and easiest way not to have as much scale or worry about bumps or some types of stains if you use Trichlor which is a Low PH sanitizer that won’t convert to oxygen molecule if your PH runs high. 

Mineral Out / Metal Chelating Agent  Used as a preventive stain treatment per directions on the bottle weekly. Amazon sells two bottles of Robelle Concentrated Mineral Out, Pool Metal Remover, Stain Remover for around $27 which should last you 5-6 months.  

Calcium Hardness  Keep your Calcium levels between 180 – 225 as much as possible to reduce scale or chalk. Both Bioguard and Natural Chemistry have scale preventive you can use to reduce the chance of scale in your salt cells, but the only easy way to remove Calcium Hardness is to drain the pool from the pump spigot, while at the same time adding water back into the shallow end of the pool at the same rate. Never leave the pool unattended to ensure the water level does not drop below the skimmer.  Test the calcium level after an hour and that will give you an idea of how many hours it will take to get your calcium level down.