API Stress Zyme

• Contains over 300 million live bacteria per teaspoonful (5 mL), supplied in a dormant state that becomes active once added to aquarium water.
• Formulated to consume sludge and organic debris, helping keep gravel and glass cleaner and supporting the tank's existing biological filter.
• Suitable for both freshwater and marine (saltwater) aquariums, and can be dosed with fish already in the tank.
• Cost per litre of treated water, based on the standard weekly dose, ranges from around 2 cents per litre in the smaller bottles down to under 1 cent per litre in the 1.89 L and 3.8 L drums – this is a per-dose figure, not a one-off yield, since Stress Zyme is dosed repeatedly rather than used once.

Litres treated per dose are calculated from the manufacturer's stated rate of 5 mL per 10 US gallons (38 L), rounded down to the nearest whole litre. Water type, active bacteria count and shelf life are as published by API; bacterial strain names and a full ingredient list are not published by the manufacturer.

Shake well before use. Using the dosing cap, add Stress Zyme via the aquarium water surface.

• Established aquariums: add 5 mL (1 teaspoonful) per 10 US gallons (38 L) of water, once weekly.
• New aquariums: double the dose at start-up and continue for 2 additional weeks before reverting to the standard weekly rate.

Weekly dosing is intended to be ongoing for the life of the aquarium, not a single treatment – the litres-treated figures above describe one dosing round, not a total lifetime yield from the bottle.

API states Stress Zyme has a 5-year shelf life and does not require refrigeration. Store the bottle upright, out of direct sunlight, and keep the cap tightened between doses. Specific manufacturer temperature limits for this exact formula are not published on the sources checked; as general practice, avoid storing any liquid aquarium additive somewhere it could freeze or overheat.

Suitable for freshwater and marine aquariums, both newly set up and established, and can be dosed while fish are present. It is a biological filtration aid, not a substitute for regular partial water changes, mechanical filter maintenance, or a treatment for fish disease – it should not be used as a medication.

API has not published a specific consumer hazard warning or first-aid statement for Stress Zyme on the sources checked. As with any aquarium additive, keep out of reach of children and pets, avoid contact with eyes, wash hands after handling, and dose only as directed on the label.

Pair with an API liquid or strip water test kit to monitor ammonia and nitrite while a new tank cycles, a dechlorinating water conditioner for use at water changes, and a gravel vacuum to physically remove the sludge the bacteria help break down.

All API products sold by Nick's Aquarium Oceanarium Terrarium are covered by the consumer guarantees under the Australian Consumer Law.

How often do I dose Stress Zyme?

Once weekly for established aquariums, at 5 mL per 10 US gallons (38 L) of water. New aquariums are dosed at double that rate for the first 2 weeks.

Can I use Stress Zyme with fish in the tank?

Yes, API's directions state it can be added while fish are in the aquarium.

Is Stress Zyme suitable for saltwater tanks?

Yes, it is labelled for use in both freshwater and marine aquariums.

Does Stress Zyme need to be refrigerated?

No. API states it has a 5-year shelf life and does not require refrigeration.

Which size should I buy?

Larger sizes carry a lower cost per litre of water treated per dose – the 1.89 L and 3.8 L drums work out to under 1 cent per litre, versus around 1-2 cents per litre from the smaller bottles – so regular users of larger tanks get better value from the bigger packs.

What exactly is in Stress Zyme?

API states each teaspoonful contains over 300 million live bacteria, supplied dormant and activated on contact with aquarium water. The manufacturer does not publish the specific bacterial strains or a full ingredient list.