pH in Marine Aquariums: Importance, Influence, and Maintenance

Introduction

pH is a critical value in marine aquariums that, unfortunately, many aquarists don't give proper attention to. Some don't even have a device for continuous 24/7 pH monitoring, instead occasionally using tests to determine pH at a specific moment. This is unacceptable if you expect to successfully maintain a marine aquarium and want to understand what's happening with the biofilter and other processes.

The Importance of pH in Marine Aquariums

Critical Importance of pH

pH is one of the most important parameters in a marine aquarium, along with salinity, temperature, and macronutrient content. If any of these parameters falls outside the "green zone," all other manipulations become meaningless.

The consequences can vary widely:

• With a small deviation — gradual suppression of corals
• With a significant deviation — rapid death of aquarium inhabitants

Optimal Range

For a marine aquarium, the optimal pH range is from 8.1 to 8.4.

Values below 8.0 or above 8.5 are unacceptable for long-term maintenance of marine organisms, especially corals.

The Role of pH in Calcification

pH is a key factor determining the possibility and rate of calcification — the process of forming coral skeletons and other calcareous structures.

Calcification is not simply calcium deposition, but a complex biochemical process involving both inorganic compounds and living coral tissues. An alkaline environment (pH above 8.1) is required for this process to proceed normally.

When pH drops below 8.1, the calcification process significantly slows down, even if all other parameters are normal. This leads to:

• Slowing or stopping coral growth
• Inability to form new skeletal elements
• Gradual degradation of existing calcareous structures when pH falls below 8.0

Factors Affecting pH

Nitrogen Cycle and Carbonate Hardness

One of the key factors affecting pH is the nitrogen cycle. During an intensive nitrogen cycle, part of the carbonate hardness (KH) is "used" in the nitrification process. Not to be confused with actual consumption.

This manifests as follows:

1. When feeding increases (system overload with organics), the nitrogen cycle accelerates
2. An accelerated nitrogen cycle requires more carbonates
3. A visible decrease in carbonate hardness occurs
4. As a result, pH may decrease

This becomes noticeable when, after prolonged increased fish feeding, you observe a sudden decrease in carbonate hardness, and after adding buffer solutions, the situation stabilizes at a new level. This indicates that the system has "adjusted" to the new load.

But with a rapid decrease in nitrogen cycle intensity, visible carbonate hardness returns and we see a sharp rise (return) of KH.

Decay Processes and Oxidizers

Besides the nitrogen cycle, pH is affected by:

• Decay processes in stagnant zones
• Release of hydrogen sulfide and other gases
• Accumulation of oxidizers in the water

Many mistakenly believe that low "acidic" pH is associated with oxygen consumption during organic decay. In reality, the process is more complex: decay releases substances (oxidizers) that actively lower water pH.

External Factors

pH is also affected by external factors:

• Carbon dioxide in the room (CO₂)
• Quality of additives and feeds used
• Operation of calcium reactors (adds acidic water to the aquarium)
• Water temperature accelerates or slows down nitrogen cycle processes, etc.

CO₂ Influence

High CO₂ concentration in the room (above 600 ppm) leads to water acidification. Sources of CO₂ include:

• Respiration of people and animals
• Household processes using open flames, such as cooking
• Insufficient ventilation

Temperature Influence

When temperature rises:

• Biochemical processes accelerate
• Gas solubility in water decreases
• CO₂ and other gas emissions increase
• As a result, pH may decrease

This explains why in summer, with increasing temperature, a slight decrease in pH is often observed.

Methods for Maintaining Optimal pH

The Right Approach to Problem Solving

Instead of fighting low pH, focus on creating conditions where pH will naturally stay in the optimal range. As they say, "don't solve the problem, create the right conditions."

Basic Ways to Maintain pH

1. Removing oxidizers from water
   • Using activated carbon for chemical filtration
   • Regular water changes
   • Ensuring good aeration and degassing
   • Effective skimming
2. Improving circulation
   • Eliminating stagnant zones
   • Ensuring good water flow through the marine system
   • Using sufficiently thick pipes for drainage and return
   • Proper placement of flow pumps
3. Controlling biological load
   • Preventing overfeeding
   • Maintaining balance between aquarium volume and number of inhabitants
   • Reasonable dosing of additives
   • Temperature control
4. Technical solutions
   • Routing the skimmer intake tube outside for fresh CO₂-free air
   • Using a CO₂ scrubber with soda lime
   • Using two-chamber calcium reactors with CO₂ burn-off chamber
   • Using quality equipment that's powerful enough

Special Attention to Substrate and Reef Structure

Anaerobic processes that negatively affect pH can occur in the substrate and inside tightly packed reef structure stones:

1. Substrate
   • Layer should not be thicker than ¾ inch (2 cm)
   • Should be constantly blown through and mixed by living organisms
   • When dirty, requires cleaning from detritus or complete washing with sea water by removing the substrate from the aquarium
2. Reef structure
   • Stones should not be tightly packed on top of each other
   • There should be sufficient water circulation inside the reef
   • Stagnant zones inside the reef structure should be avoided

Preventive Measures

Proper system planning from the start will avoid many pH problems:

1. Sufficient pipe diameter for water return
   • For systems up to 60 gallons (220 liters) — 25 mm
   • For systems over 55 gallons — 32 mm
   • For systems over 250 gallons (1000 liters) — 40 mm and above
2. Powerful skimmer
   • Should match the system volume
   • Provide effective organic removal and gas exchange
3. Parameter control system
   • Constant pH monitoring
   • Regular measurement of carbonate hardness
   • Temperature control

Conclusion

pH is not just one of the water parameters, but an integral indicator of the entire system's condition. Maintaining pH in the optimal range (8.1-8.4) is critically important for successful marine aquarium keeping, especially with corals.

Instead of fighting low pH, focus on creating the right conditions: good circulation, effective filtration, oxidizer removal, and biological load control. This comprehensive approach to system organization will allow maintaining a stable and optimal pH level without constant intervention.

Proper system planning from the start will help avoid many future problems. Unfortunately, many aquarists first learn "how not to do it" instead of initially learning "how to do it right."