Article: pH in planted aquariums

If you're having trouble changing your pH, it's likely that you have a buildup of buffers or acids (or both!) in your system.  These can hold your pH in place despite repeated additions of buffers.  In planted systems, Seachem® only recommends carbonate-based buffers like Alkaline Buffer™ and Acid Buffer™, so here are some tips for shifting your pH in these types of aquariums.

If your pH is too low:

1. Check your alkalinity. This is a measure of how resistant your pH is to change, and will go up when you add buffers like Alkaline Buffer™ to the system.  Your alkalinity is probably too low to counteract the amount of acids in your tank which are holding your pH down.  If your alkalinity is too low, dose more Alkaline Buffer™ (and Acid Buffer™, if you are using them together to target a specific pH).
2. Do regular water changes.  One of the primary causes of low pH in a freshwater system is a buildup of organic acids in the aquarium.  Regular water changes with clean water dilute down these acids and prevent this depression of the pH.
3. Address acid sources in the aquarium.  Logs, peat moss, organic material, and certain kinds of aqua-soils will leach organic acids into the aquarium over time.  Likewise, CO2 injection systems acidify the water over time.  These acid sources need to be balanced by a sufficiently high KH.  If you find that you have significant acid sources in your aquarium that are depressing the pH, you will need to maintain a higher alkalinity (use more Alkaline Buffer™ and Acid Buffer™) to hold your pH at your desired level.

If your pH is too high:

1. Check your alkalinity.  This is a measure of how resistant your pH is to change, and will go up when you add buffers like Alkaline Buffer™ to the system.  Your alkalinity is probably quite high, and is resisting the influence of your Alkaline Buffer™ and Acid Buffer™.  We recommend to either seek out low-alkalinity source water and carry out water changes to dilute the buffers, or to do small, regular doses of Acid Buffer™ (testing your pH after every dose) until your pH is at or near your desired level.  Then, dose Alkaline Buffer™ and Acid Buffer™ together according to the ratio chart on the bottle to "set" your pH and prevent it from falling further.
2. Avoid overusing buffers.  If your alkalinity (KH) is too high, it will tend to drag your pH upward.  As with all things in fish-keeping, moderation is key when trying to maintain a stable pH.
3. Address buffer sources in the aquarium.  Certain types of substrate, rocks, decorations, and filter medias will leach buffers into the water that raise your pH.  If you are trying to maintain a low pH, you will need to opt for decorations and substrate that will not do this.