Water Conditioners & pH

API pH Down

FreshwaterPlant safe

API pH Down is the liquid for nudging freshwater pH downwards when a test reads higher than your fish need. It is colourless, leaves the water clear and contains no phosphate or nitrate, so it gives algae nothing to grow on. The dose is deliberately small: 1 ml for every 38 litres, followed by another pH test before any second dose. That slow approach matters, because many fish cannot cope with a swing of more than 0.2 in a day. Jungle Aquatics carries the 37 ml and 118 ml bottles.

Size: 37 ml

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Live pricing and stock on jungleaquatics.com — purchase through Jungle Aquatics, with delivery across South Africa.

Dosage calculator

Enter your aquarium volume and the calculator works out how much API pH Down to use for each rate on the pack.

Aquarium volume

Measured in

Use the water the tank actually holds, less substrate and decor.

Single dose1 ml per 38 litres
Enter a volumeRetest before any further dose; keep changes under 0.2 pH per 24 hours

Test with an API pH kit first, and never chase a big correction in one go.

A guide only — always follow the dosing instructions printed on the pack, and measure with the bottle's cap or a syringe rather than by eye.

Technical details

Product type	Liquid pH reducer
Sizes	37 ml and 118 ml
Dose	1 ml per 38 litres, then retest before any further dose
Maximum safe change	0.2 pH per 24 hours for sensitive fish
Suitable for	Freshwater aquariums
Safe with	Fish and live plants
Form	Colourless liquid; phosphate- and nitrate-free
Water clarity	Does not cloud the water
Made by	Mars Fishcare, USA

Measure pH with an API pH Test Kit before and after every dose — never dose to a guess.

How far will one dose lower my pH?

Less than you might expect, by design. Add 1 ml for every 38 litres of water, wait for it to mix, and test again before you consider a second dose. How big the step is depends on your carbonate hardness (KH): soft water drops readily, while hard, well-buffered water resists and may need repeated daily doses. Keep the total change under 0.2 pH in any 24 hours — the limit the label gives for sensitive fish. A 100-litre tank takes just under 3 ml per dose, so the 37 ml bottle is plenty for occasional corrections and the 118 ml suits larger tanks or regular adjustment.

Moves pH downward a little at a time

One dose of 1 ml per 38 litres lowers the pH by a small step rather than a leap. Fish adapt to gradual change far better than to a sudden drop, so the label asks you to test again before adding a second dose and to keep any change within 0.2 per 24 hours. It suits the soft, slightly acidic conditions tetras, rasboras and many South American species prefer.

Clear water and nothing for algae to eat

The formula is colourless and does not cloud the tank, so a dosed aquarium looks exactly as it did before. It is also free of phosphate and nitrate, the two nutrients most pH products leave behind, which means correcting pH will not set off a green-water bloom a week later.

Safe for live plants

API confirms that pH Down and pH Up are both safe in planted aquariums, so a planted tank that has drifted alkaline can be brought back down with the plants in place. Keep to the dose and retest between additions; plants dislike sudden swings as much as fish do.

Correction, not control

pH Down shifts pH; it does not hold it there. If your tap water is hard and strongly buffered, the pH will climb back between water changes and you will be dosing constantly. In that case the better tool is a Proper pH buffer that locks the value in, or softening the water first with the Water Softener Pillow.

Frequently asked questions

Can I use pH Down in a marine aquarium?

It is formulated for freshwater. Marine water is far more strongly buffered and needs a marine-specific approach, so keep pH Down for freshwater tanks.

Why does my pH keep rising again after I use pH Down?

Hard, alkaline tap water is buffered and will pull the pH back up between water changes. Test your KH; if it is high, soften the water or use a Proper pH buffer to hold the value rather than repeatedly dosing a liquid.

Is it safe to dose pH Down every day?

Yes, once a day is acceptable as long as you test pH between doses and the total change stays within 0.2 per 24 hours. Never add a second dose without testing first.

Will pH Down cause algae or cloudy water?

No. It is colourless, does not cloud the water and contains no phosphate or nitrate, so it adds nothing algae can feed on.

Is API pH Down available in South Africa?

Yes — both the 37 ml and 118 ml bottles are available from Jungle Aquatics in Fourways, Johannesburg, with delivery nationwide; live pricing and stock are on jungleaquatics.com.

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South Africa's leading pet and aquarium store since 2007 — with the API range on the floor in Fourways, advice from people who test water every day, and easy ordering from anywhere in the country.

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