pH Buffers

When it comes to aquarium water chemistry, few numbers get as much attention as pH. For many aquarists—especially beginners—there’s a natural instinct to “correct” pH using store-bought buffers. The logic seems sound: fish like a specific pH, so you should match that number exactly. But like many things in aquarium keeping, the reality is more nuanced. In many cases, pH buffers cause more harm than good, leading to sudden pH swings or feeding nuisance algae through nutrient imbalances.

This page isn’t about demonizing all pH buffers—there are some cases where they're useful—but rather about helping you understand when and why buffering might be doing more harm than good.

What Are pH Buffers?

A pH buffer is a chemical solution added to your aquarium to stabilize or change the pH. Typically, these products are designed to either lower, raise, or lock your tank’s pH into a specific range. They work by increasing the water’s buffering capacity using specific chemical compounds (often phosphate-based) to resist pH shifts. There are natural components of typical water that work to stabilize the pH, such as carbonates, however each buffering compound will tend towards a different pH from one another, which is why there are different buffers for different pH levels. That increased buffering capacity from commercial buffers helps prevent wild swings, which is a good thing—until it isn't.

The Problem with “Chasing Numbers”

The first major issue with pH buffers is the mindset that leads to their use: trying to hit a specific pH number instead of maintaining a stable one. Many fishkeepers see that their species "prefers a pH of 6.8–7.4" and assume they need to adjust their water to match that exactly. But most tank-bred and tan-raised fish are already adapted to a wide range of stable conditions, and minor deviations outside the “ideal” range don’t cause harm. Sudden pH swings, on the other hand, can absolutely be lethal.

The irony here is that a well-meaning aquarist who doses a pH buffer may actually destabilize the tank instead of stabilizing it. Unless you're testing carbonate hardness (KH), phosphates, and understand how your water chemistry interacts with your buffer, you're dosing blind—and that's when crashes happen. A poorly calculated dose or competing chemistry (like soft water with low KH) can lead to sharp drops or spikes in pH within hours. Fish don’t die from a "bad" pH—they die from change.

Nutrients in Disguise

Another overlooked issue is the makeup of many commercial pH buffers. A large number of these products—especially the ones that “lock” pH at 7.0—are phosphate-based. Phosphates are a powerful buffer in water chemistry, but in an aquarium, they're also a key nutrient for algae.

By trying to stabilize your pH, you may be dosing your tank with exactly what algae love to eat.

This isn’t just theory. Many aquarists struggling with mysterious algae blooms eventually trace the source back to buffering agents, fertilizers, or pH stabilizers that are adding excess phosphates. Even if your test kits don’t show massive spikes (because algae are consuming the phosphate as it’s introduced), the effect still plays out in the tank.

This becomes especially problematic in planted tanks, where plants already require a balanced ratio of nutrients. By adding phosphate-heavy buffers, you're skewing that ratio—and algae are happy to take advantage.

When Buffers Might Be Necessary

That said, there are cases where buffering makes sense—particularly in specialized setups:

• African cichlid tanks often need hard, alkaline water that mimics the mineral-rich lakes they come from. In this case, crushed coral or aragonite substrates (a natural buffer) are more reliable and safer than liquid chemicals.

• Breeding softwater species, such as certain tetras or killifish, may require adjustments to water hardness and pH using RO (reverse osmosis) water and gentle buffering agents. Even then, it’s a slow, carefully measured process—never a quick fix.

In these setups, buffering is part of a holistic water management plan—not an impulse reaction to a test strip result.

The Better Approach: Stability Is The Goal

For the vast majority of community tanks, the best thing you can do is leave the pH alone—as long as it’s stable. Your fish will adapt to a pH of 6.5, 7.2, or even 8.0, so long as it’s consistent and within a reasonable range. Trying to “fix” a number with additives often introduces more instability, not less.

If you're concerned about your pH dropping over time, the root cause is often a drop in KH due to biological activity (like nitrification and CO₂ buildup). Regular water changes with a stable water source are usually enough to keep pH from drifting dangerously.

Final Thoughts

pH buffers can look like a quick solution to a perceived problem, but in most cases, they're a shortcut with hidden costs. They can spike nutrient levels, fuel algae outbreaks, and create sudden chemical swings that do more damage than a slightly off-target pH ever would.

Instead of chasing a number, chase balance. Let your aquarium evolve into a stable ecosystem, supported by consistent maintenance and thoughtful choices. Your fish don’t need perfection—they need stability.