Your underwater critters and plants depend on your vigilant watch over their water's chemistry. Among other essential tasks, you have to keep the water pH steady at the appropriate reading. Because pH tends to drop over time, you must stay on the offensive.
Use an electronic pH meter or a water testing kit to regularly read your tank's pH level. Take readings at the same time of day whenever you do them, because pH has a natural pattern of fluctuations throughout the day. Calibrate your meter as recommended in the manufacturer's instructions to maintain its accuracy. Replace test kits after one year, as their accuracy diminishes over time.
Perform partial water changes every two weeks to help maintain steady chemistry and keep the pH up where you want it. Always prepare a bucket of water in advance to add to the tank. If you have a marine ecosystem, mix in salt to your target gravity. Treat the water with any conditioners or other products you use, and bring it to the tank temperature. Siphon out 10 to 15 percent of your aquarium's water and replace it with new water.
Stir 1 level teaspoon of baking soda per gallon of replacement water into your prepared new water during a partial water change if testing reveals pH has dropped and you need to give it a boost. Add this water into your aquarium bit by bit over an hour, rather than pouring it all in at once as you would with a standard partial water change.
Include live plants in your aquarium to consume carbon dioxide in the water, as too much of this gas is a leading cause of dropping pH.
Install a fountain or other device that disturbs the surface of your tank water if you don't have a trickle filter. This effectively enhances water aeration to keep a healthy balance of oxygen and carbon dioxide in the water, helping maintain your pH.
Add an air stone, a bubble wand or another aerating device to your aquarium if your filtration system doesn't circulate the water much, if you don't have an accessory or equipment that disturbs the water's surface, or if your tank water is 80 degrees Fahrenheit or warmer.
Attach a protein skimmer to your aquarium if you have a saltwater system. Clean its tray out daily. An efficient protein skimmer removes detritus and helps keep carbon dioxide levels where they should be to keep pH levels up.
Keep your aquarium in a well-ventilated room. If it's a small space or if it has little fresh air circulation, open a window or use fans to circulate air from outside the room. Too much atmospheric carbon dioxide can prevent proper aeration at the surface of the tank water, leading to an excess of the gas in the tank system -- and perpetually falling pH.
Eric Mohrman has been a freelance writer since 2007, focusing on travel, food and lifestyle stories. His creative writing is also widely published. He lives in Orlando, Florida.