How pH Affects the Health of Your Koi and Goldfish

pH is an extremely important pond water parameter that needs to be monitored, corrected (if need be) and stabilized.  pH naturally fluctuates with the lowest readings in the morning and the highest readings in the evening.  This fluctuation, however, should be gradual and not more than a single digit.  Koi and goldfish live best in water with a 7.0 to 8.0 pH. 

Monitoring pH

Simple pH test kits are available for ponds and water gardens.  Do not use pH test kits for pools.  We prefer drop test kits because they are easier to read and tend to be more accurate.  They also do not cost an arm and a leg.  We use (and sell) the test kits by PondCare which can be purchased separately or as part of the Master Liquid Drop Test Kit.  Other more sophisticated test kits are available for the professional or advanced koi-keeper.

The pH should be tested about once a week normally - give or take - or any time that the fish are acting strangely or a fish dies.  New ponds should be tested more often.  The stability of the pond (also called alkalinity) should also be tested and stabilized with a pH stabilizer if necessary.

High pH

The higher the pH the more alkaline it is.  If pH was temperature a high pH would feel cold.  To give you an idea of how high pH feels -- imagine how your hands feel when you are writing on a chalkboard.  Your hands are dry and chalky because the chalk has a high pH.  This same principal applies to the fish.  The chalkiness could make the skin peel.  High pH is definitely a stress factor and harms the health of fish and also plants.

Another problem that high pH has is that it makes ammonia more toxic.  If the pH is low the ammonia is less toxic.  .5 ppm of ammonia might not normally kill fish but if the pH is high it may just do it!

Cement and some kinds of rock can make the pH go up.  Cement ponds are guaranteed to have high pH for several months and up to a year or more.  Even waterfalls with cement poured between the rocks leach out and push the pH up.  Eventually the properties that push the pH up will leach out and stabilize but that's not any comfort to the koi or goldfish who have to live in the high pH.

To correct high pH we need to lower it and lock it into place.  Use pH Down (it has great directions and you'll know how much to use) or use household vinegar or muratic acid.  Be careful with muratic acid - it can bring the pH down too low and too quickly!  For that reason we advise to use vinegar.  It's much more forgiving.  Remember that if you have fish in the pond not to shock them by suddenly bringing down the pH.  Do it in increments about a half hour apart and then, once you have it lower than 8.0 - preferably low 7's - lock it into place with stabilizer.

Low pH

Low pH of around 6.5 and 6.8 is not so much a problem as long as it doesn't take a sudden nose dive.  It still is not good to have a constant low pH so it should be corrected.  Low pH is acidic and burns the gills of the fish

Want to be dropped into a vat of acid?  That's what a pH crash might feel like to a fish.  If pH was temperature a low pH would feel hot.  This, of course, will also make the skin of the fish peel.  The pH is at its lowest point in the wee hours of the morning.  If you wake up to a pond filled with dead fish and the pH is testing low your pond has just experienced a pH crash. 

A pH crash is quite a problem because not only does it kill the fish it kills the nitrifying cycle in the pond and makes you have to literally start the ecosystem of your koi pond or watergarden all over again.  Because it is such a problem we've dedicated a whole page just for pH Crashes.  Click HERE to go there.

Stabilizing the pH

If the water stays a little higher or stays a little lower it doesn't hurt as much as when the pH swings wildly from highs to lows within a 24 hour period.  Stability, therefore, is the most important part of pH.  Larger bodies of water stay more stable than smaller ones.  Aquariums are more apt to have unstable pH than a pond.  Our koi ponds and water gardens are less stable than a natural lake or pond.  Stabilizing a small pond is pretty easy.  Just add pH stabilizer.  Some people use marble chips for its stabilizing properties but we have a very easy to use powder that does the trick and lasts for most the season or until you change the water. 

More Information About pH

• Getting the Swing Out of pH
• The Importance of Water Parameters

Items You Might Need:

Master Liquid
Drop Test Kit

pH Down

pH Up

pH Test Kit

pH Stabilizer

Doc's De-Chlorinator

Know Your Gallons!

Heavy Duty Water Meter

© copyright, 2008, PondDoc.com.  Reproduction or use of any content on this website prohibited without written consent from PondDoc.com.  This advice is given free of charge and serves as information only to help you with determining the cause of fish health problems.  The content given is to be used as guidelines only.  By following the guidelines on our website you are agreeing that we will not be held responsible or liable for any losses.  We cannot diagnose your specific case.  We are simply forwarding the benefit of our extensive experience with koi and goldfish health.