Water Chemistry Basics (pH, KH, GH)

The three numbers that matter: pH, KH, and GH

Water is not just H₂O; it is a solvent carrying dissolved ions that dictate biological function. You must understand the relationship between pH, KH, and GH.

pH (Potential Hydrogen)

This measures the acidity or alkalinity of the system on a logarithmic scale.

• The Scale: 7.0 is neutral. Below 7 is acidic; above 7 is alkaline.
• The Stability Rule: Fish can adapt to a wide range of pH, but they cannot handle rapid fluctuations. A swing from 7.0 to 6.0 is a 10x increase in acidity, which can cause osmotic shock and death.

KH (Carbonate Hardness / Alkalinity)

Think of KH as the "Shield" or Buffer Capacity that protects your pH.

• The Mechanism: Acids (from fish waste and nitrification) naturally push pH down over time. Carbonates (KH) neutralize these acids.
• The Crash: If KH drops to 0°, your pH "shield" is gone. The water will plummet rapidly into extreme acidity (pH < 5.0), killing the bio-filter and the fish. This is a common cause of "Old Tank Syndrome."
• Target: Keep KH above 3–4 dKH to ensure a stable pH.

GH (General Hardness)

This measures the concentration of divalent metal ions, primarily Calcium (Ca²⁺) and Magnesium (Mg²⁺).

• Biological Function: Fish use these ions for osmoregulation (balancing internal fluids) and bone development. Shrimp and snails require GH to build their exoskeletons.
• Deficiency: Low GH leads to "molting issues" in shrimp and stunted growth in livebearers.

Making tap water safe

Municipal water is engineered to be sterile, making it toxic to aquatic life.

Chlorine vs. Chloramine

• Chlorine (Cl₂): A gas that evaporates naturally.
• Chloramine (NH₂Cl): A stable compound of chlorine and ammonia used by most modern water treatment plants. It does not evaporate.
• The Protocol: You must use a water conditioner (Dechlorinator) that specifically breaks the chlorine-ammonia bond.
• Mechanism: Sodium Thiosulfate neutralizes the chlorine, but releases the ammonia. High-quality conditioners (like Seachem Prime) then temporarily bind that free ammonia for 24–48 hours until your bio-filter can process it.

Keeping nitrate down

In a closed system, matter is neither created nor destroyed. Fish food becomes waste, which becomes Nitrate (NO₃⁻). Unlike in nature, nitrates do not magically disappear; they accumulate until they become toxic or stunt growth.

The Fractional Water Change

The solution to pollution is dilution.

• The Standard: Change 15–30% of the water volume weekly.
• The Math: If your Nitrates are at 40ppm and you change 50% of the water, you reduce Nitrates to 20ppm.
• Temperature Matching: Always match the temperature of the new water to the tank water (±2°F) to prevent thermal shock, which induces "Ich" (white spot disease).

Substrate Vacuuming

Nitrates originate from decaying organic matter in the gravel.

• The Tool: Use a gravel vacuum (siphon) to pull water through the substrate.
• The Goal: Remove the brown sludge (detritus) without removing the beneficial bacteria living on the gravel surface.

Spotting drift before it hurts fish

Move from reactive "fire-fighting" to proactive engineering using the app's Health Lab.

Nitrate & TDS Accumulation Projection

Instead of guessing when to change water, use the AI algorithm.

• The Forecast: The Health Lab analyzes your stocking density and filtration capacity to predict when your system volume will hit critical toxicity levels.
• TDS (Total Dissolved Solids): As water evaporates, minerals stay behind. Over months, TDS creeps up, hardening the water. The Lab tracks this "hardness creep" and suggests larger water changes to reset the mineral balance.

Hardware Wear Prediction

• Filter Health: As biomass accumulates in your filter, flow rate decreases. The Health Lab analyzes your turnover rate vs. bioload to predict "Clogging Intervals".
• Action: If the Lab shows "Filter Media Health" at <50%, schedule a maintenance session to rinse your sponges in old tank water before the flow stops completely.

The "Prototype" Warning

Remember, the Health Lab is a Prototype Algorithm designed for estimation.

• Verification: Always verify the prediction with a liquid test kit. If the AI predicts safe water but your fish are gasping, test immediately. Biological systems are chaotic; algorithms are linear.