API AMMO-LOCK Aquarium Ammonia Detoxifier, 1 Gallon

API AMMO-LOCK Aquarium Ammonia Detoxifier is a 1-gallon freshwater and saltwater aquarium water treatment. It detoxifies ammonia, chlorine and chloramines, converting toxic ammonia into a non-toxic form that the biological filter can then process in the usual way. The 1-gallon (3.8 L) bottle is the largest AMMO-LOCK size API produces, sized for large tanks, fish rooms, breeding setups and anyone dosing regularly or keeping a bottle on hand for an ammonia emergency. This 1 gallon size is used at 5 mL per 10 gallons of aquarium water, in freshwater or saltwater.

AMMO-LOCK does not remove ammonia from the water. It locks ammonia into a non-toxic form, which is why an ammonia test can still read positive after dosing — that result is expected, not a failure. It is explained in full below. Keep testing, and keep your normal water-change routine.

How API AMMO-LOCK works

API states that AMMO-LOCK “does not remove ammonia; it converts it to a non-toxic form; so, even though ammonia is in a safe, non-toxic form, aquarium will still test positive for ammonia until it is removed by the biological filter.” The non-toxic ammonia is then removed by the biological filter, or aquarium cycle, in the usual way.

The same dose also acts on tap-water contaminants: AMMO-LOCK detoxifies ammonia, chlorine and chloramines, which makes it usable both as an emergency response to an ammonia reading and as a treatment for water added during a change.

Three things AMMO-LOCK is not, so the product is used the way API intends:

• Not an ammonia remover. The ammonia stays in the water in a converted form.
• Not a replacement for the biological filter. The filter is what actually clears the ammonia; AMMO-LOCK protects fish while it does.
• Not a replacement for water changes. API still recommends a 25% water change after dosing.

Why can an ammonia test still read positive after AMMO-LOCK?

This is the single most common question about the product, and the answer is straightforward.

Why it happens: a standard aquarium ammonia test kit measures the total amount of ammonia in the water. AMMO-LOCK changes the form of that ammonia, not the amount of it. The ammonia is still in the tank, so the test still finds it and reports it.

What it means: in API's own words, the “aquarium will still test positive for ammonia until it is removed by the biological filter.” A positive reading after dosing is the expected result. It is not evidence that the bottle failed, that the dose was too small, or that the test kit is faulty.

What API says to do next:

1. Continue dosing 5 mL per 10 gallons every 2 days until ammonia is not detected.
2. Perform a 25% water change after dosing — API recommends this in addition to the treatment.
3. If ammonia is still present after 7 days, perform a partial water change, service your filter, and reduce feeding.

The reading comes down when the biological filter processes the ammonia and water changes export the rest — not when the detoxifier is dosed. If you are working through a reading right now, our step-by-step guide to high ammonia in an aquarium covers the full order of operations.

API AMMO-LOCK dosage

Directions from the API label, quoted in full:

“Use dosing cap bottle. Add 5 ml per 10 gallons (38 L) of aquarium water. Add every 2 days until ammonia is not detected. If, after 7 days, ammonia is still present, perform a partial water change, service your filter, and reduce feeding.”

Doses above are the API label rate of 5 mL per 10 gallons applied to common tank sizes. Always follow the directions printed on your bottle.

A 25% water change is still recommended after dosing.

How to use API AMMO-LOCK

1. Test the aquarium water and note the ammonia reading.
2. Measure 5 mL of AMMO-LOCK per 10 gallons of aquarium water using the dosing cap.
3. Add the dose to the aquarium.
4. Repeat every 2 days until ammonia is no longer detected.
5. If ammonia is still present after 7 days, perform a partial water change, service the filter and reduce feeding.

Freshwater and saltwater use

AMMO-LOCK is labelled for both freshwater and saltwater aquariums. The dose rate is the same in either: 5 mL per 10 gallons of aquarium water, repeated every 2 days until ammonia is not detected.

How AMMO-LOCK compares with Seachem Prime

Both are aquarium water treatments that detoxify ammonia rather than removing it, and both are labelled for freshwater and saltwater and handle chlorine and chloramine. The published differences are the scope of the claims (Seachem also publishes nitrite and nitrate detoxification; API's AMMO-LOCK page does not), the label dose rate, and the available bottle sizes — API publishes a 1-gallon format, Seachem's largest listed retail size is 4 L.

We have set both manufacturers' published claims side by side, with a source named for every row, in our neutral comparison of API AMMO-LOCK and Seachem Prime. No head-to-head performance testing has been published by either manufacturer, so that page compares stated specifications rather than declaring a winner.

Product specifications

Frequently asked questions

What does API AMMO-LOCK do?

It detoxifies ammonia, chlorine and chloramines in freshwater and saltwater aquariums. Ammonia is converted into a non-toxic form rather than being removed from the water.

Does API AMMO-LOCK remove ammonia from aquarium water?

No. API is explicit on this point: AMMO-LOCK converts ammonia to a non-toxic form; it does not remove it from the water. Removal is done by the biological filter, supported by water changes.

Why does my ammonia test still show ammonia after using AMMO-LOCK?

Because the ammonia is still present, just in a non-toxic form, and a test kit measures the total amount rather than the form. In API's words, the “aquarium will still test positive for ammonia until it is removed by the biological filter.” See the dedicated section above for what to do next.

How much API AMMO-LOCK should I use?

Add 5 mL per 10 gallons (38 L) of aquarium water using the dosing cap, every 2 days until ammonia is not detected. The chart above applies that rate to common tank sizes.

How often can API AMMO-LOCK be used?

Every 2 days until ammonia is no longer detected. If ammonia is still present after 7 days, API directs you to perform a partial water change, service the filter and reduce feeding.

Can API AMMO-LOCK be used in freshwater aquariums?

Yes. AMMO-LOCK is labelled for freshwater aquarium use.

Can it be used in saltwater aquariums?

Yes. The same product and the same dose rate are labelled for saltwater aquariums.

Do I still need to perform water changes?

Yes. A 25% water change is still recommended after dosing, and the label directs a partial water change if ammonia persists beyond 7 days. A water change is the step that physically removes ammonia from the tank.

Can AMMO-LOCK be used with biological filtration?

Yes — the biological filter is what finishes the job. API states the non-toxic ammonia “is then removed by the biological filter, or aquarium cycle, in the usual way.”

What size aquarium is the 1-gallon bottle suitable for?

Any size — the dose scales with the tank, so the format is a question of how much you dose rather than how large your aquarium is. At the label rate of 5 mL per 10 gallons, one US gallon of AMMO-LOCK (about 3,785 mL) covers roughly 7,570 gallons of aquarium water in total. This figure is calculated from the label dose, not a manufacturer claim, and actual coverage depends on how many repeat doses a tank needs. In practice the 1-gallon size suits large tanks, multi-tank fish rooms, breeders and retailers rather than a single small aquarium.

Why not just use Seachem Prime?

Both products detoxify rather than remove ammonia, and neither manufacturer has published head-to-head testing. The differences that are documented — claim scope, dose rate and formats — are set out with sources in our AMMO-LOCK vs Seachem Prime comparison.

Source for all API claims on this page: API (Mars Fishcare) official AMMO-LOCK product page and directions for use.

Related reading

• High Ammonia in an Aquarium: What to Do — causes, emergency order of operations and prevention.
• API AMMO-LOCK vs Seachem Prime — a sourced, side-by-side comparison of both manufacturers' published claims.
• Fish & Aquatics — water treatments, test kits, filters, heaters and aquarium accessories.