Too much Stabilizer: A chlorine lock can occur when you have added too much
Essentially, a chlorine lock means that the chlorine in your pool is not working as it should to sanitise the water. This issue is brought about by the presence of too much cyanuric acid, which can overpower the free chlorine in your pool.
The best way to break a chlorine lock is to shock your pool and achieve breakpoint chlorination. You triple shock your pool with ``unstabilized chlorine.''
You have one of two issues. 1) your CYA levels aren't high enough so the sun is destroying your chlorine faster than you can keep putting it in or 2) and more likely is that you have chlorine demand. So something that takes awhile to get a handle on is that a tester kit can only test from 0 chlorine and up.
Two different chemical agents that can reduce chlorine levels are Sodium Thiosulfate and Pool-Grade Hydrogen Peroxide (specific to pool treatment). Be sure to test your water after using one of these agents as they tend to impact pH, sometimes dramatically.
The most common chemical to neutralize chlorine and chloramine is potassium metabisulfite, or Campden tablets (Campden tablets sometimes use sodium instead of potassium but the final result is the same). These tablets are often used in brewing operations to achieve the same disinfection results and remove chlorine.
Direct sunlight (UV)
Direct sunlight breaks down chlorine. Without a stabilizer (cyanuric acid) in the water, as much as 90% of free available chlorine could be destroyed within just two or three hours.
The consistent inability to maintain chlorine levels is also called “chlorine demand” and is most often caused by a high level of inorganic and organic contaminants in the water. Those contaminants force the chlorine to work extremely hard to oxidize them, leaving little chlorine to protect swimmers.
"Shocking” refers to the process of adding chlorine or non-chlorine pool chemicals to the water in order to raise the "free chlorine” level. The goal is to raise this level to a point where contaminants such as algae, chloramines and bacteria are destroyed.
Unbalanced pH: Unbalanced pH in your pool water can also be a factor for a chlorine lock in your pool water.
So, to answer the question, if your Total Chlorine is high but Free Chlorine is low, it is an indication that the hot tub requires a shock treatment. This can be done by adding your weekly dose of an oxidizer like Dazzle Amaze or Mineraluxe Oxygen.
Too much stabilizer can cause your chlorine to become less effective at killing bacteria and algae, and it can also lead to cloudy or hazy and unsafe pool water. Additionally, high stabilizer levels can cause your pH levels to become imbalanced, which can lead to other water quality issues.
The fastest and most accepted way to break a chlorine lock is by shocking your pool and achieving breakpoint chlorination. This is done by triple shocking your pool with UNSTABILISED CHLORINE. Don't use stabilised chlorine as the added cyanuric acid will worsen the problem.
Your best bet is to triple shock it with calcium hypochlorite. To triple shock, add 3 pounds of shock per 10,000 gallons of water. You'll need to know your pool's volume to do this correctly, which you can determine with a pool calculator.
Bacteria, algae and microscopic contaminants, such as urine, sweat, sunscreen and beauty products, take a toll on your swimming pool's water chemistry. These substances, when present in your pool water, accelerate chlorine demand and can affect your chlorine's ability to maintain properly sanitized water.
Algae, bacteria, or fungus growth. Debris or contaminants from winter or periods of inactivity. Heavy pool usage or high bather load, especially during summer. Biofilm or organic material in the water, such as sunscreen, leaves, or algae.
Test Your Water Regularly, Especially During High Temperatures: Extreme heat can throw off your pool's water balance, leading to issues like increased pH levels and chlorine depletion. Regular testing with HTH™ Pool Care 6-Way Test Strips will help ensure proper pH, chlorine, alkalinity, and other chemical levels.
It's usually caused by a high level of inorganic and organic contaminants in the water. Those contaminants force the chlorine to work extremely hard to oxidize them, leaving little chlorine to protect swimmers. Proper chlorine levels cannot be reestablished without first eliminating the contaminants.
Sodium ascorbate will also neutralize chlorine. It is pH neutral and will not change the pH of the treated water. Sodium ascorbate is preferable for neutralizing high concentrations of chlorine.
Low/No chlorine production
The factors that affect chlorine levels include the summer heat, poor filtration, bather load, and the frequency of use. It's also possible that the time period you set is too short, the chlorine output level is too low, or the filter needs backwashing.
The effect of excess chlorine in pools is an alteration in pH levels of pool water, making it more acidic. Signs of high chlorine levels can include itchy sensations in the eyes, nose and throat, nausea, vomiting, dizziness, lung irritation, and skin rashes.
The main purpose of water conditioners is to break down chlorine and chloramine and make water safe for fish to inhabit. Almost all dechlorinators contain sodium thiosulfate, which reacts to chlorine and chloramine to form harmless byproducts.
Sun Exposure (UV Rays): Ultraviolet rays from the sun can break up free chlorine very quickly. Without stabilizers (such as cyanuric acid), chlorine is less effective, and its levels fall more rapidly in outdoor pools.