What Is Chlorine and Chloramine — and Why Is It in Your Tap Water?
The Phnom Penh Water Supply Authority treats municipal tap water with disinfectants before it reaches your home. This is excellent news for human health — it prevents cholera, typhoid, and bacterial contamination from spreading through aging pipes across the city. The two main disinfectants used are chlorine and chloramine, and both serve the same purpose: killing microorganisms in the water supply so that the water is safe to drink by the time it reaches your tap.
Chlorine is the older and simpler of the two. It is a reactive gas dissolved into water as a disinfectant, and it does its job well in short pipe runs. However, chlorine is volatile — it off-gasses relatively quickly when exposed to open air or sunlight. This gave rise to the popular belief that leaving water in a bucket overnight will make it safe for fish. In shorter pipe systems or less humid climates, that method had some validity decades ago.
Chloramine is a compound formed by combining chlorine with ammonia. Water authorities, including those managing Phnom Penh's expanding distribution network, began switching to or supplementing chlorine with chloramine because it is far more stable. It does not off-gas. It persists in the water for days, resists evaporation, and travels reliably through long pipe runs without losing its disinfecting power. For a growing city like Phnom Penh with an aging and expanding pipe network, chloramine is increasingly the practical choice for water safety.
The critical problem for aquarium keepers is that Phnom Penh tap water now commonly contains both chlorine and chloramine, and their concentrations can vary depending on your district, the time of year, and how recently your local pipes were flushed. You cannot see, smell, or taste chloramine at typical municipal concentrations. Assuming your water is safe because it looks clear or because it sat in a bucket last night is one of the most common and costly mistakes aquarium owners in Cambodia make.
- ✦Never assume tap water quality is consistent — Phnom Penh concentrations vary by district and season.
- ✦Purchase a basic chlorine/chloramine test strip pack from your local aquarium shop to check your own tap water at least once.
- ✦If you are near a major distribution junction or in a newer development area, chloramine concentrations tend to be higher.
How Chlorine and Chloramine Destroy Your Aquarium
When untreated tap water enters an aquarium, both chlorine and chloramine begin attacking biological tissue almost immediately. Fish absorb water and dissolved chemicals directly across their gill membranes — a surface that is extraordinarily thin and highly permeable by design, because oxygen exchange depends on it. Chlorine and chloramine are oxidizing agents, and they do not distinguish between a bacterial cell in a water pipe and the delicate gill cells of your betta, guppy, or arowana. They burn through the same way.
The damage to gill tissue is progressive. In low concentrations, fish may initially appear stressed — rapid breathing, hovering near the surface, flashing against tank walls. At higher concentrations or with extended exposure, the gills begin to swell and hemorrhage, oxygen absorption drops, and the fish begins to suffocate despite being surrounded by water. In heavily chlorinated tap water added directly without treatment, sensitive fish like cardinal tetras or discus can show signs of distress within minutes and die within hours.
The second point of attack is your biological filter. The nitrifying bacteria that colonize your filter media — Nitrosomonas and Nitrospira species — are the heart of the nitrogen cycle. They convert toxic ammonia from fish waste into nitrite, and then into the far less harmful nitrate. These bacteria are living organisms, and chlorine and chloramine kill them just as effectively as they kill pathogens in a water pipe. A single large, untreated water change can crash your biological filter, causing an ammonia spike that kills fish days after the water change itself.
For Cambodian fishkeepers dealing with tropical temperatures between 28 and 35 degrees Celsius, the biological impact is compounded. Warmer water holds less dissolved oxygen, meaning fish are already working harder to breathe. Adding even mild gill damage from low-level chloramine exposure on top of heat stress pushes fish much closer to their physiological limits. What might be a recoverable stress event in a cooler climate can become a fatality in a Phnom Penh dry-season tank running at 33 degrees.
- ✦Watch for rapid gill movement and surface hovering after any water change — these are early signs of chemical stress.
- ✦Never do a water change of more than 30% with untreated water, even if you plan to add dechlorinator after — treat the bucket first.
- ✦In hot months (March-May), your fish are already heat-stressed. Any additional chemical stress during this period is much more dangerous.
The Dangerous Myth of Overnight Aging — What It Can and Cannot Do
Generations of aquarium keepers have passed down the advice to age your tap water in a bucket for 24 hours before adding it to a tank. This practice originated when municipal water supplies used only free chlorine, which is genuinely volatile. Left in an open container, free chlorine will off-gas into the atmosphere over several hours, and by 24 hours a significant portion will have dissipated — particularly if the water is warm and the container is shallow and exposed to sunlight or a moving fan.
The problem is that chloramine does not behave this way at all. Chloramine is chemically stable. You can leave water in a bucket for 24 hours, 48 hours, or even 72 hours and the chloramine concentration will remain nearly unchanged. There is no practical amount of sitting time that removes chloramine without chemical intervention. Boiling water will remove it, but boiling enough water for a meaningful water change is impractical and drives off dissolved oxygen as well.
In Phnom Penh, where the water authority uses chloramine to maintain disinfection through a city-wide distribution network, relying on the overnight aging method is genuinely dangerous. Many experienced fishkeepers in Cambodia have lost fish they could not explain — fish that died days after a routine water change from what appeared to be a mysterious bacterial or oxygen issue. In many of these cases, the culprit was chloramine slowly stressing the fish and damaging the biological filter across multiple water changes.
Aged water is not useless. Letting tap water sit does allow temperature equalization, which is valuable in Cambodia where cold pipe water introduced to a warm tank creates rapid temperature swings. It also allows any particulate to settle and gives trace dissolved gases time to equilibrate. But aged water is not safe water unless you have confirmed through testing that your local supply uses free chlorine only — and in Phnom Penh today, you cannot safely assume that.
How Dechlorinators Work — The Chemistry Behind the Bottle
A dechlorinator is a chemical solution added to tap water before it enters the aquarium. The active chemistry depends on what the product is designed to neutralize. For free chlorine, the classic and most proven agent is sodium thiosulfate. This compound reacts with chlorine in a straightforward neutralization reaction, converting it into chloride ions — the same harmless chloride present in natural water. The reaction is nearly instantaneous, which is why sodium thiosulfate-based dechlorinators work within seconds of mixing.
Chloramine is chemically more complex to neutralize because the chlorine and ammonia components are bound together and do not separate through simple oxidation. Products designed to handle chloramine typically use a reducing agent such as sodium hydroxymethanesulfinate, which breaks the chlorine-ammonia bond. This releases both components in a neutralized form — the chlorine is rendered harmless, and the ammonia is either neutralized directly or converted to a non-toxic form. Some premium products go further and detoxify the released ammonia component as well.
The quality difference between products lies in what else they do beyond basic dechlorination. Basic sodium thiosulfate products neutralize chlorine quickly and inexpensively but do nothing for chloramine, heavy metals, or biological stress compounds. Mid-range products add chloramine neutralization and often include aloe vera extracts or polymer-based slime coat replacements, which help fish recover their natural mucus barrier after the stress of a water change. Premium products add ammonia and nitrite detoxification on top of everything else.
It is worth understanding that dechlorinators do not filter water — they chemically transform specific harmful compounds into harmless ones. They do not remove heavy metals from old pipes unless specifically formulated to do so, they do not adjust pH, and they do not add minerals. A dechlorinator treats the biological safety of the water for fish; water parameters like hardness, pH, and temperature still need to be managed separately. In Cambodia, where well water and filtered water are also common in homes, always confirm what type of water source you are treating before choosing a product.
- ✦Read the label of any dechlorinator carefully — many budget products handle only free chlorine, not chloramine.
- ✦Sodium thiosulfate alone is not sufficient for Phnom Penh tap water. Ensure your product explicitly states chloramine neutralization.
- ✦Add dechlorinator to your bucket before adding the fish tank water — mix it through the new water first, not directly into the tank.
Products Available in Cambodia — What to Buy and What to Expect
Seachem Prime is widely regarded as the gold standard water conditioner for serious aquarium keepers, and it is available in Cambodia through specialist aquarium shops in Phnom Penh, typically ranging from around $8 to $12 USD (approximately 32,000 to 48,000 KHR) for a 100 ml bottle. Prime neutralizes both free chlorine and chloramine, detoxifies ammonia, nitrite, and nitrate temporarily, and promotes slime coat recovery. Its highly concentrated formula means a single small bottle treats a very large volume of water — 5 ml per 200 liters is the standard dose — making it economical despite the upfront price.
Tetra AquaSafe is the most widely available water conditioner in Cambodia and can be found in most aquarium shops and some pet sections of larger supermarkets in Phnom Penh and Siem Reap. It retails at approximately $4 to $7 USD (16,000 to 28,000 KHR) depending on bottle size. AquaSafe neutralizes chlorine and chloramine, adds a vitamin B complex to reduce transport stress, and includes a polymer to support the fish's natural protective slime coat. It is a reliable mid-range choice that handles the essentials competently.
Generic dechlorinators sold in small unlabeled bottles at local fish markets and street-side aquarium shops around Phnom Penh markets are typically sodium thiosulfate solutions of variable concentration. These are inexpensive — often 1,000 to 3,000 KHR per bottle — and effective against free chlorine only. If you are buying fish from a local market and need a quick treatment for transport water, these can serve that immediate purpose. However, they should not be your primary dechlorinator for routine water changes if your tap water contains chloramine.
A note on local market products: Cambodia's aquarium supply chain does not always have consistent quality control. Products imported informally may have degraded in transit due to heat exposure (a real risk in containers crossing Southeast Asia in 35-degree weather), may have expired date codes obscured, or may be diluted compared to their labeled concentration. When buying from smaller shops, look for products in sealed, clearly labeled packaging with intact caps, and be cautious of unusually cheap pricing on products that should cost significantly more. Investing in a reputable brand from a dedicated aquarium store is worth the extra cost.
- ✦Seachem Prime's ammonia-detoxification feature makes it particularly valuable during the cycling phase of a new tank.
- ✦Store all liquid water conditioners away from direct sunlight and heat — a shelf in an air-conditioned room is ideal in Cambodia's climate.
- ✦When in doubt about a product's authenticity, purchase from established aquarium specialty stores rather than general markets.
Correct Dosing, the Prime Double-Dose Method, and Ammonia Emergencies
Correct dosing is non-negotiable. Under-dosing a dechlorinator is one of the most common mistakes aquarium keepers make, and it is particularly tempting when a bottle is running low. If the standard dose for your product is 5 ml per 100 liters, dosing 2 ml and hoping it is enough is not a calculated risk — it is a gamble with your fish's gill tissue. Always measure accurately. A small plastic syringe or graduated dropper, available at any pharmacy in Cambodia for a few hundred KHR, makes precise dosing easy and removes the guesswork from eyeballing drops.
Seachem Prime has a well-documented and manufacturer-supported double-dose protocol for emergencies. If you test your water and find elevated ammonia — whether from an uncycled tank, an overloaded filter, or a water change that crashed your beneficial bacteria — you can dose Prime at double the standard rate: 10 ml per 100 liters instead of the standard 5 ml. At this concentration, Prime temporarily detoxifies ammonia up to approximately 1 ppm, converting it to a non-toxic form that your biological filter can still process. This protection lasts approximately 24 hours.
The double-dose emergency method is exactly that — an emergency tool, not a management strategy. It buys you 24 hours to perform a proper water change, identify and fix the source of elevated ammonia, and stabilize your tank. If you are reaching for double-dose Prime more than once a week, the underlying problem is likely an overstocked tank, an underpowered filter, overfeeding, or a cycling issue that needs to be properly resolved. In Cambodia, where high ambient temperatures accelerate bacterial decomposition and oxygen depletion, ammonia problems tend to escalate faster than in cooler climates.
Always treat the new water in its container before adding it to the tank, not the reverse. Adding dechlorinator to the tank after pouring in tap water means your fish and filter bacteria are exposed to chlorine or chloramine for the seconds or minutes it takes for the chemical to mix and react throughout the tank volume. Treat the bucket, stir gently, wait 60 seconds, then pour. This small change in habit costs nothing and eliminates a brief but real stress event for your fish during every single water change.
- ✦Keep a dedicated measuring syringe next to your dechlorinator bottle so you never estimate a dose.
- ✦Prime double-dose is a 24-hour emergency bridge — always follow it with a proper water change and root-cause fix.
- ✦In a heavily stocked tank during Cambodia's hot months, test ammonia before and after water changes to catch spikes early.
Managing Water Quality in Cambodia's Climate — Heat, RO Water, and Smart Habits
Cambodia's tropical climate creates water management challenges that fishkeepers in cooler countries rarely face. Temperatures between 28 and 35 degrees Celsius are normal year-round, and during the dry season from March through May, outdoor temperatures in Phnom Penh regularly exceed 37 degrees. Water in tanks without chillers or consistent air conditioning will track ambient temperature closely. At these temperatures, dissolved oxygen drops, evaporation accelerates, and the concentration of any dissolved compounds — including residual chloramine or ammonia — effectively increases as water volume decreases.
Reverse osmosis (RO) water represents the premium approach to water quality management. An RO unit removes virtually everything from tap water — chlorine, chloramine, heavy metals, dissolved solids, and minerals — producing essentially pure water. Because fish need specific mineral content depending on the species, RO water is then remineralized using products like Seachem Equilibrium, Salty Shrimp mineral salts, or similar products to restore the precise water chemistry required. This approach gives you complete control over your water parameters and eliminates any concern about varying chloramine levels in Phnom Penh tap water.
RO units are available in Cambodia, primarily through aquarium specialty shops and water treatment suppliers in Phnom Penh, typically starting from around $80 to $150 USD for a basic under-sink unit. For fishkeepers maintaining multiple tanks, breeding sensitive species like discus or wild-caught altum angels, or keeping shrimp that require precise mineral parameters, the investment pays off quickly in reduced losses and better results. For casual keepers with a single community tank, a quality dechlorinator used consistently is a practical and sufficient alternative.
For everyday water changes in Cambodia, the most effective habit is simple consistency. Pre-treat every bucket of replacement water with your chosen dechlorinator at full label dose before it enters the tank. Match the temperature of the new water to the tank temperature before adding — a 3 to 5 degree temperature difference during a water change stresses fish noticeably in tropical species. Keep your dechlorinator bottle next to your water change supplies so it is never forgotten. These are not complicated steps, but done consistently at every water change, they are the single most reliable protection against preventable fish loss.
- ✦During Cambodia's hot season, top up evaporated water daily with treated water — evaporation concentrates everything left behind, including any residual compounds.
- ✦If you use a household RO drinking water filter for your tank, check that it is not a filter that only removes sediment — it must include an RO membrane to remove chloramine.
- ✦Match new water temperature to tank temperature within 2 degrees before adding — use a basic thermometer, which costs around 5,000 KHR at any aquarium shop.
Building a Safe Water Change Routine — and Where to Find Trusted Products
A reliable water change routine does not require expensive equipment or complicated chemistry knowledge. It requires three things done consistently: treating new water before it enters the tank, matching the temperature, and doing water changes regularly enough that no single change needs to be a large, stressful event. For most tropical community tanks in Cambodia, a 20 to 25 percent weekly water change with properly dechlorinated water — done every week without exception — is more valuable than occasional large water changes done inconsistently.
The water conditioner you choose matters less than the habit of using it correctly every time. Seachem Prime is the most capable product available in Cambodia and offers the best value per liter of water treated given its concentration. Tetra AquaSafe is a solid and accessible alternative that handles the essentials well. Generic sodium thiosulfate solutions from local markets are acceptable only if you have confirmed your water source uses free chlorine only — in Phnom Penh, that confirmation is increasingly difficult to obtain with certainty. When in doubt, choose a product that explicitly handles both chlorine and chloramine.
New fishkeepers in Cambodia often underestimate how much of their early losses come from water chemistry errors rather than disease or incompatible fish choices. Most fish sold at local markets in Phnom Penh have already been through significant stress — transport from farms in Thailand, Vietnam, or local grow-out operations, holding at market conditions, and then transport again to your home. These fish arrive with compromised immune systems and damaged slime coats. Adding them directly into untreated tap water, even briefly, can push already-stressed fish past recovery. A quality water conditioner used at the receiving stage is as important as using it during routine water changes.
At 4848 One Shop, we carry Seachem Prime, Tetra AquaSafe, and a curated selection of water treatment products chosen specifically for the conditions Cambodian fishkeepers face — Phnom Penh's chloramine-treated tap water, high ambient temperatures, and the varied quality of locally available fish. Our team can advise you on dosing for your specific tank size, help you understand your water parameters, and recommend the right conditioner for the fish you are keeping. Good water care is the foundation of every successful aquarium, and we are here to help you get it right from the very first water change.