pH and aquariums: why it is the key to healthy underwater life

A stable pH value is perhaps the most underestimated factor in the aquarium hobby. While many aquarium enthusiasts focus on temperature and feeding, the acidity of the water determines whether fish, plants and beneficial bacteria actually thrive. In this blog we take a deep dive into the world of pH, from the biological necessity to the latest measuring equipment, and look at how Meytec products help keep your aquarium in balance.

Why is pH important for an aquarium?

The pH value indicates how acidic or alkaline the water is, on a scale of 0 to 14. A value of 7 is neutral, lower is acidic and higher is alkaline. But why does this matter so much?

For fish: stress, disease and death

Fish are extremely sensitive to pH fluctuations. A deviation of more than 0.3 pH per day can already cause stress. That stress lowers resistance, makes fish susceptible to disease and in serious cases can even lead to death. In addition, an incorrect pH has a direct influence on the toxicity of ammonia: the higher the pH, the more ammonium converts into toxic ammonia; especially above pH 7.5 the proportion of ammonia increases rapidly. Ammonia is fatal even in small amounts.

For plants: nutrient uptake and growth

Aquatic plants only absorb nutrients well within a certain pH range. At the wrong acidity, essential minerals such as iron and manganese can precipitate, so that plants can no longer absorb them. The result: yellowed leaves, stagnating growth and eventually dying plants. Plants also influence the pH themselves: during the day plants absorb CO₂, causing the pH to rise; at night they release CO₂, causing the pH to fall.

For water quality and the biological filter

The beneficial bacteria in your filter – responsible for converting ammonia into nitrate – work best at a stable pH. Extreme values slow down nitrification, causing harmful substances to build up. A stable pH is therefore not only important for the fish, but for the entire ecosystem in your aquarium.

Big overview: which fish species needs which pH?

The ideal pH differs greatly per fish species. Roughly speaking, there are three categories:

South American species (soft, acidic water)

• Discus: pH 5.5–6.5
• Neon tetras: pH 5.0–7.0
• Cardinal tetras: pH 5.5–7.0
• Dwarf cichlids (Apistogramma): pH 5.5–6.5
• Corydoras: pH 6.0–7.5

Asian and African species (slightly acidic to alkaline)

• African cichlids (Malawi/Tanganyika): pH 7.8–8.5
• Barbs: pH 6.0–7.5
• Danios: pH 6.5–7.5
• Rasboras: pH 6.0–7.0

Community aquarium (widely applicable)

• Most community fish and plants thrive best between pH 6.8 and 7.4
• Goldfish: pH 7.0–7.6
• Livebearers (guppies, platies, swordtails): pH 7.0–8.0
• Angelfish: pH 6.5–7.5

Important: choose fish that suit the pH of your tap water, instead of constantly trying to adjust the pH. A stable pH is more important than an “ideal” pH.

How do you measure pH in an aquarium?

There are several methods for measuring the pH value in an aquarium, each with advantages and disadvantages:

Test strips or drop tests

Cheap, but often inaccurate and subjective due to colour interpretation. Suitable for a rough indication, but not for precision work.

Portable pH meter (handheld)

A compact device that measures the pH value quickly and accurately. Ideal for periodic checks: daily, weekly or whenever you suspect something is wrong. The meter gives a digital value immediately and is easy to calibrate. The portable pH meter GT-500PH is a fast and accurate pH meter that lets you measure the correct pH value in no time and is easy to calibrate automatically.

Fixed pH measuring and control system (pH probe)

A permanently installed system in which the pH probe sits continuously in the aquarium water or in a flow cell. The system measures continuously and can even control the CO₂ supply. The pH probe is the sensitive and most critical component here – a high-quality electrode, correctly maintained and properly calibrated, determines the reliability of your measurements.

The Meytec NXG-PH probe is a durable pH probe with a fast response that is compatible with the majority of systems on the market.

pH dosing devices

Advanced systems that not only measure, but also automatically dose pH correction solution. They combine a pH controller with a dosing pump and are ideal for demanding aquariums. Take a look at Meytec’s pH probes and pH buffer solutions for reliable pH measurement in your aquarium.

Top pH brands in Europe: models and Meytec compatibility

Important: the Meytec NXG-PH probe is compatible with any device that has a BNC input and accepts an electrode with a diameter of 12 mm.

Meytec GT-500PH and NXG-PH: your pH partners

Meytec offers two products that are perfectly suited to the needs of the aquarium hobbyist:

Meytec GT-500PH pH meter

The GT-500PH is a compact digital pH meter that measures pH from 0.00 to 14.00 with a precision of ±0.05. It has a built-in temperature sensor with automatic temperature compensation and a dust-tight housing that is resistant to water jets (IP65, not for full immersion) – ideal for use around the aquarium. Automatic calibration at pH 7, pH 4 and pH 10 makes the device user-friendly, even for beginners. Batteries (4× LR44) are included.

Meytec NXG-PH pH probe

The NXG-PH is a professional pH probe with a BNC connection, a diameter of 12 mm and a 3 metre cable. It measures pH 0.00–14.00 with a precision of 0.01 pH and works at temperatures of 0–80°C. The double junction and double Ag/AgCl reference ensure stable, reliable measurements.

Compatibility: where do these Meytec products fit?

The GT-500PH is a standalone handheld meter: it works independently and can be used immediately in any aquarium.

The NXG-PH is compatible with, among others:

• Hanna Instruments (pH controllers and meters with BNC input)
• Milwaukee Instruments (pH controllers)
• Mettler Toledo (devices with BNC input)
• JBL (pH measuring systems)
• Bluelab (pH controllers)

Maintenance and calibration: the key to accuracy

A pH probe is a sensitive sensor. With the right maintenance, you can extend its service life considerably:

• Always store the probe in the protective cap with KCl 3 mol/l storage solution. Never in demineralised water, never dry
• Clean the probe with cleaning solution to remove deposits (max. 15 minutes), always before calibration
• Calibrate when you first use it and regularly after that. First pH 7, then pH 4 or pH 10. Follow the manual of your meter or dosing system

Conclusion

With its BNC connection, 12 mm diameter and 3 metre cable, the Meytec NXG-PH probe is a universal pH probe that is compatible with most pH measuring and control systems on the European market. Whether you use a JBL PROFLORA pH-Control Touch, sera seramic pH Controller, Aqua Medic pH computer set, Hanna controller, Milwaukee dosing system or Bluelab pH Controller: as long as your device has a BNC input and accepts a 12 mm electrode, the NXG-PH is an excellent choice.

For correct calibration, use the Meytec buffer solutions: pack pH 7 + pH 10 + 475 mV for two-point calibration on the alkaline side, pH 4 + pH 7 for the acidic side, or pH 4 + pH 7 + 475 mV for systems that also measure ORP. Do not forget to store the probe in KCl 3 mol/l storage solution after use and to clean it with the Meytec cleaning solution before calibration.