Do hard water fish need KH?

Joshaeus

Member
Or is it the general hardness they are more concerned about? I understand that softwater fish care more about KH/carbonate levels than GH levels, but wasn't sure whether that was the case with hardwater fish like african cichlids and guppies (which you'd think would liberally use that general hardness). Thanks
 

wishuponafish

Member
No, GH is what they mostly care about but raising KH will also raise GH and makes it easier to keep pH high.
My tap water is strange with high GH/pH and a KH of 1-2 dKH, and my livebearers and hardwater fish do very well.
 
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Joshaeus

Member
wishuponafish said:
No, GH is what they mostly care about but raising KH will also raise GH and makes it easier to keep pH high.
GH only measures molecules in the water containing calcium and magnesium, while KH measures molecules containing carbonates...increasing KH would not affect GH at all unless the carbonate containing molecule also contains calcium or magnesium (calcium carbonate, for example...though that molecule does not dissolve easily in water).
 

wishuponafish

Member
Joshaeus said:
GH only measures molecules in the water containing calcium and magnesium, while KH measures molecules containing carbonates...increasing KH would not affect GH at all unless the carbonate containing molecule also contains calcium or magnesium (calcium carbonate, for example...though that molecule does not dissolve easily in water).
Yes, technically raising KH by itself somehow will not affect GH, but most methods of raising KH in an aquarium will involve carbonates bound to an electrolyte which will raise GH I believe.
 

Chanyi

Member
wishuponafish said:
Yes, technically raising KH by itself somehow will not affect GH, but almost all methods of raising KH in an aquarium will involve carbonates bound to an electrolyte which will raise GH.
Which methods would this be? Most if not all methods I have seen are based of carbonate(s) linked usually to potassium - KHCO3 or K2HCO3.

For hardwater fish, I think they prefer both a relative amount of KH and GH in the water, and most tapwater scenarios that have a higher pH / KH usually have a higher GH as well, making it very nice for "hardwater" fish species.
 

wishuponafish

Member
Chanyi said:
Which methods would this be? Most if not all methods I have seen are based of carbonate(s) linked usually to potassium - KHCO3 or K2HCO3.

For hardwater fish, I think they prefer both a relative amount of KH and GH in the water, and most tapwater scenarios that have a higher pH / KH usually have a higher GH as well, making it very nice for "hardwater" fish species.
I may be mistaken, but I think I read somewhere that electrolytes other than just Ca and Mg such as K and Na also contributed to GH to some degree.
Whether they show up in GH readings or not, these other electrolytes do matter to fish as they play a role in their osmoregulation (which is a big part of why GH matters). That's why salt treatment using pure NaCl works, as the Na ions change the osmotic balance for both fish and disease-causing microorganisms.
 

Whitewolf

Member
Any water that has alot of hardness but low KH can cause rapid PH swings and get acidic fast as the bioload organic matter builds up in the aquarium.
 

candiedragon

Member
Pretty interesting question. It did not dawn on me that soft water fish care about kH more, but it makes sense because the goal is to keep the kH low to creat a more acidic environment and you need to keep the kH in control as not to trigger a pH swing.

I will preface the following by saying I don't have any science or physical evidence to back me up. It is purely based on my experience and the experience of long-time hobbyists in my local community who share their wisdom.

It is hard to say what is more important (I am leaning towards gH being more important) but perhaps what I share on the subject of guppies in Hawaii might help towards a conclusion. Here, it is believed that fancy guppy strains do best with neutral to slightly acidic pH (6.8-7.2) and very hard water, which is generally what our water is like anyway. I generally just make sure that my gH levels are maintained and that seems to do the trick. There are some people who live in certain areas of the island (they're on a different water source) that don't do well since their water is a lot more acidic so they usually have to supplement with crushed coral or something which does raise kH as it is calcium carbonate and therefore raises pH. I did get some guppies from a shop in such conditions (I test bag water to determine whether or not I should do a slow acclimation) and they were wonderfully healthy before and after I brought them home. Their pH was around 9.0, they were in the tank they usually put their african cichlids but I guess they're changing things around because the shop is now under new ownership as of a month ago. I believe that tank has a crushed coral substrate that's why. So it seems to me that pH doesn't matter as much, the main thing is that the guppies have a super hard water.
 

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