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To keep things really simple; pH is basically just a “test” you run to get a result you need to have. And you need to run it. That bears repeating. You need to run pH tests periodically in the care of your fish pond. One of the most common water quality problems in ponds is a “low pH”. You don’t typically want your ponds’ pH to drop below 6.8 and frankly, when the pH is below seven, it should serve as a warning sign that your pH is at risk to “crash”. “pH Crash” is a sudden drop in pH which kills a lot of fish in this hobby every year. If you do not buffer the carbonates in your pond, you will experience this phenomena sooner or later.
Here’s a list of things which drag your pH in a downward (acidic) direction. Fish and plant respiration produces carbon dioxide which forms carbonic acid, which lowers your pH. Animal, food and plant wastes decay and release carbon dioxide. Reduction of the primary fish waste product; Ammonia releases hydrogen ions which reduce pH quite a bit.
So you might ask; “What ever is it that supports or keeps pH from falling?” The answer is “carbonates”. Carbonates (also called buffers) will equalize or neutralize all those elements which drag down the pH. When the carbonates are used up, the pH proceeds in its downward direction and the fish die.
“Where do carbonates come from?” Commercially available “buffers” supply the needed carbonates. They are chemically formulated to do it intelligently without wild swings in pH. They are formulated to raise the carbonates, which supports the pH but not too high. Some contain phosphoric acid to keep the pH from climbing too high. An equillibrium is engineered into the product. Pretty cool. You can use Baking Soda, but I’ve found this to be a really short-lived “fix” and it an push the pH too high. Baking Soda is poorly sustained in the water. You’ll be adding it often. Buffers are formulated to last longer.
“Can you add too much carbonate?” Yes, you can. We don’t want carbonate alkalinity levels over 300 ppm. Now, it’s not an emergency if you have numbers that high, the real question would be if those numbers were consistent, then you would see gill problems.
I guess this would be the appropriate place to mention that pH has a critical relationship with Ammonia. You can read more about Ammonia shortly. When the pH of the water is high, or higher than seven, you should be aware that Ammonia accumulations are more toxic. THis means that you might have some low level of ammonia in your pond and because your pH is quite high (like nine) the Ammonias are very toxic. Your neighbor has a higher Ammonia level than your pond has, but his fish are fine! The reason is that his pH is lower, making the Ammonia less toxic even though it’s in higher accumulations.
Do NOT raise your pH rapidly in the presence of Ammonia accumulations. Better to do a major water change and remove the Ammonia, and let the replacement water raise the pH. Then you could use a pH Buffer to support the PH where you want it.
“What is pH Crash?” This is a really common situation which kills a lot of fish every year. People fail to realize that the pH is “just a number for the moment” supported in real life by carbonates. They keep checking their pH and it shows “fine” so they dismiss it. After a while, the carbonates which actually create and support the pH are used up (exhausted) and the pH crashes down to 5.5 very suddenly, killing a lot of the fish. The person assumes it’s a parasitic problem and starts adding medications without checking the pH because the pH has been “fine” for weeks. When they finally realize the pH is crashed, they don’t raise the pH fast enough, and kill the rest of their fish. When your pH crashes, raise that pH at once!!!
SHORT AND SWEET: Always use a “pH Buffer” regularly. If you’re feeling “advanced” you can start testing for and record your carbonate alkalinity so you can predict the eventual behavior of the pH which it creates and supports.