Why Your Aquarium pH Crashes: KH Explained (Animated), by Art's Fish Room on YouTube. 2 min 10 s.
- Video length
- 2 min 10 s
- Time to do it
- 20 minutes
- Difficulty
- Easy
- Steps
- 8
What you need
Steps
Test your tap water with a liquid GH and KH test kit before you change anything. Write down both numbers in degrees so you have a baseline to compare against later.
Know the difference between the two. GH is calcium and magnesium, which shrimp need for moulting and snails need for strong shells. KH is carbonate, which buffers pH and holds it steady.
Test the tank water every week. When KH falls to 2 dKH or below the buffer is used up, and pH can crash overnight, so act before you get there.
To raise KH and GH, rinse a handful of crushed coral and put it in a media bag inside your filter. It dissolves slowly and lifts hardness over several days.
To lower hardness, mix RO water with your tap water at water changes. Start with one quarter RO water, then test GH and KH again to see where you landed.
Change part of the water on a regular schedule. Fresh water replaces the carbonate minerals your tank uses up, which stops KH drifting down between changes.
Pick fish that suit your tap water instead of fighting your water chemistry. Soft water fish struggle in hard water, and hard water fish struggle in soft water.
Move hardness slowly. Shifting GH or KH by more than a couple of degrees in a single day stresses fish, shrimp and snails, so adjust over a week or more.
Tips and common mistakes
Do not chase an exact pH number. Keep KH stable and the pH will stay steady on its own.
Crushed coral works gradually, so give it about a week before you add more.
Test strips are hard to read at low KH, so use a liquid kit when the number really matters.
Fish gasping at the surface in the morning often means a pH crash, so check KH before adding anything.
Questions
What KH should my aquarium have?
Keep KH above 2 dKH, because that is where the buffer runs out and pH becomes unstable. Many freshwater tanks sit comfortably between 3 and 8 dKH.
Does crushed coral raise pH as well as KH?
Yes. Crushed coral adds carbonate, which raises KH, and a higher KH usually holds the pH higher and steadier. Add a small amount and test before adding more.
Why did my pH drop after a water change?
If your replacement water has very low KH, it dilutes the buffer in the tank and pH can fall. Test the KH of your tap water and mix in minerals if it reads near zero.
This guide was drafted from the video's details and general task knowledge. It has not been checked against the full video. Check the video and relevant product instructions before following a procedure. Report a correction.
