pH & KH in Planted Aquariums
pH levels tend to fluctuate in planted aquariums – particularly by injection of pressurised CO2. These pH swings can also occur in natural water bodies as carbon dioxide concentrations build up overnight from decomposition of organic matter.
These changes tend to occur relatively quickly, both in nature and the home aquarium, as plants receive light (whether sunlight in the morning or artificial aquarium lighting) and quickly begin using the available CO2.
In nature, none of the fish or plants are affected by these pH swings of up to 1 full point – so do you need to worry about your pH levels in the home aquarium?
Not really! Most of the commonly available fish species for keeping in home aquariums will not be affected by minor swings in your pH levels, and neither will your plants. Fish are able to adapt to pH levels providing the swings are not rapid and dramatic.
With that said, there are more sensitive fish species that come from isolated bodies of water, where these pH swings are less common. Wild caught species from smaller waterways may be more sensitive to fluctuations, so exercise caution accordingly if you are keeping these types of fish.
Bacteria is also generally unaffected by pH swings and low pH levels as they are able to adapt fairly easily to changing parameters.
KH – The Real Concern
pH is directly affected by KH, or Carbonate Hardness. The KH of your aquarium is determined by the amount of Carbonate and Bicarbonate ions in your water. With more carbonates in your water, your PH will be higher and also more stable.
The stability comes from the level of carbonates – when acidic water, tannins or other products are added to the aquarium water, the level of carbonates is reduced, and so the pH is also reduced. With more carbonates in your water, pH is reduced to a lesser degree. If your KH is low (less than 1dKH for example), there is less buffer and so pH levels will be affected more easily.
You can increase or decrease the KH in your tank by using additives or natural solutions such as crushed coral, which will in turn increase or decrease your pH depending on your goals. On the other hand, if the pH level fluctuates in your aquarium the KH level will not be significantly altered. For example, using pressurised CO2 will reduce your pH but does not reduce KH.
The problem with fluctuations in KH is that fish are affected by these changes. The concentration of carbonates affects their osmoregulation – their ability to maintain an internal balance of salt and water.
Because fluctuations in KH directly affect pH levels, it can be easy to assume the changing pH level is to blame for issues. The reality is that pH swings with no change in KH will not harm your livestock.
Maintaining KH stability is much more important than chasing a particular pH – without one, you’ll never get the other. If your pH is mostly stable it’s a good indication your KH is also stable.
So pH doesn’t matter?
Not exactly. There are fish and plant species that prefer certain pH levels to remain healthy. With that said, these species will more importantly need a specific KH range. Some Cichlid spp. for example are said to prefer a high pH, but will live happily in an aquarium with a pH of 7 as long as your KH is high. They need it for osmoregulation!
That’s not to say that pH levels don’t play a role in the health of your plants and livestock. When pH drops to levels outside of a species’ natural living conditions, this can cause problems. It’s not the change in level, but the extremity of the pH value itself that causes issues.
For example, as previously mentioned a cichlid that prefers a pH around 8.5 will cruise happily in a ph of 7, providing KH levels are high. But, if your pH starts at 7 and drops below 6, this is outside of the cichlid’s natural range and you will see health problems arise. The same goes for the other direction – a betta that prefers more acidic water will not tolerate higher pH long-term.
What’s the best pH for Fish and Plants?
Most fish available for the home aquarium will do just fine with a pH between 6-8. If you’re keeping fish species such as cichlids that prefer a higher pH, maintaining your KH level at around 3dKH will stop your pH from getting too low. For fish that prefer a more acidic pH, the level can be reduced with acids but this will also affect your KH. Injecting pressurised CO2 will reduce your pH without affecting KH, but only while the CO2 injection is running. If your water is not already in the preferred range of your chosen livestock, it is easier to choose more suitable livestock for your parameters than constantly chase a specific range.
Plants generally prefer more acidic conditions with a pH between 6-7. This is not to say plants won’t do well with a pH between 7-8, they just won’t have optimal conditions in the more alkaline range, so you won’t see their best growth form. There are also some more picky plant species that prefer low pH, low KH and high GH.
More common plant species are not so fussy and can be grown in alkaline water, even above a pH of 8, with no real preference for a specific KH range.
It’s always a good idea to research the fish and plant species you are planning on keeping to ensure you can provide them with the best conditions for their health.
pH levels tend to fluctuate in planted aquariums – particularly by injection of pressurised CO2. These pH swings can also occur in natural water bodies as carbon dioxide concentrations build up overnight from decomposition of organic matter.
These changes tend to occur relatively quickly, both in nature and the home aquarium, as plants receive light (whether sunlight in the morning or artificial aquarium lighting) and quickly begin using the available CO2.
In nature, none of the fish or plants are affected by these pH swings of up to 1 full point – so do you need to worry about your pH levels in the home aquarium?
Not really! Most of the commonly available fish species for keeping in home aquariums will not be affected by minor swings in your pH levels, and neither will your plants. Fish are able to adapt to pH levels providing the swings are not rapid and dramatic.
With that said, there are more sensitive fish species that come from isolated bodies of water, where these pH swings are less common. Wild caught species from smaller waterways may be more sensitive to fluctuations, so exercise caution accordingly if you are keeping these types of fish.
Bacteria is also generally unaffected by pH swings and low pH levels as they are able to adapt fairly easily to changing parameters.
KH – The Real Concern
pH is directly affected by KH, or Carbonate Hardness. The KH of your aquarium is determined by the amount of Carbonate and Bicarbonate ions in your water. With more carbonates in your water, your PH will be higher and also more stable.
The stability comes from the level of carbonates – when acidic water, tannins or other products are added to the aquarium water, the level of carbonates is reduced, and so the pH is also reduced. With more carbonates in your water, pH is reduced to a lesser degree. If your KH is low (less than 1dKH for example), there is less buffer and so pH levels will be affected more easily.
You can increase or decrease the KH in your tank by using additives or natural solutions such as crushed coral, which will in turn increase or decrease your pH depending on your goals. On the other hand, if the pH level fluctuates in your aquarium the KH level will not be significantly altered. For example, using pressurised CO2 will reduce your pH but does not reduce KH.
The problem with fluctuations in KH is that fish are affected by these changes. The concentration of carbonates affects their osmoregulation – their ability to maintain an internal balance of salt and water.
Because fluctuations in KH directly affect pH levels, it can be easy to assume the changing pH level is to blame for issues. The reality is that pH swings with no change in KH will not harm your livestock.
Maintaining KH stability is much more important than chasing a particular pH – without one, you’ll never get the other. If your pH is mostly stable it’s a good indication your KH is also stable.
So pH doesn’t matter?
Not exactly. There are fish and plant species that prefer certain pH levels to remain healthy. With that said, these species will more importantly need a specific KH range. Some Cichlid spp. for example are said to prefer a high pH, but will live happily in an aquarium with a pH of 7 as long as your KH is high. They need it for osmoregulation!
That’s not to say that pH levels don’t play a role in the health of your plants and livestock. When pH drops to levels outside of a species’ natural living conditions, this can cause problems. It’s not the change in level, but the extremity of the pH value itself that causes issues.
For example, as previously mentioned a cichlid that prefers a pH around 8.5 will cruise happily in a ph of 7, providing KH levels are high. But, if your pH starts at 7 and drops below 6, this is outside of the cichlid’s natural range and you will see health problems arise. The same goes for the other direction – a betta that prefers more acidic water will not tolerate higher pH long-term.
What’s the best pH for Fish and Plants?
Most fish available for the home aquarium will do just fine with a pH between 6-8. If you’re keeping fish species such as cichlids that prefer a higher pH, maintaining your KH level at around 3dKH will stop your pH from getting too low. For fish that prefer a more acidic pH, the level can be reduced with acids but this will also affect your KH. Injecting pressurised CO2 will reduce your pH without affecting KH, but only while the CO2 injection is running. If your water is not already in the preferred range of your chosen livestock, it is easier to choose more suitable livestock for your parameters than constantly chase a specific range.
Plants generally prefer more acidic conditions with a pH between 6-7. This is not to say plants won’t do well with a pH between 7-8, they just won’t have optimal conditions in the more alkaline range, so you won’t see their best growth form. There are also some more picky plant species that prefer low pH, low KH and high GH.
More common plant species are not so fussy and can be grown in alkaline water, even above a pH of 8, with no real preference for a specific KH range.
It’s always a good idea to research the fish and plant species you are planning on keeping to ensure you can provide them with the best conditions for their health.
