What should I do?

Why it matters

High pH makes ammonia more toxic — more of it turns into the harmful un-ionized form as pH rises. Tank 4 also shows ammonia at 0.6 mg/L, which raises the risk. In tanks and ponds with algae, pH often peaks in the late afternoon.

What to check next

1. Re-test with a fresh sample to confirm (calibrated meter or fresh test reagents).
2. Note the time of day: an afternoon high that drops by dawn usually points to algae/photosynthesis.
3. Check alkalinity — last reading 70 mg/L. Low alkalinity lets pH swing widely.
4. Re-check ammonia (last 0.6 mg/L) — ammonia toxicity rises as pH rises.
5. Check your source/top-up water pH and any recent additives (lime, buffer, salt, treatments).

Do now

• Increase or verify aeration and water circulation where appropriate.
• Reduce or hold feeding while ammonia or oxygen is a concern — uneaten feed adds ammonia.
• Consider a partial water exchange only if your source water is known to be suitable (pH, temperature, chlorine-free).
• Do not add acid, lime, buffer or any chemical by guesswork. Any adjustment needs your system volume, the exact product, your current alkalinity and the product label instructions.

pH — last 7 readings