KH and GH

[JayLB]

Can someone tell me what is the purpose of knowing the KH and GH.

Does this change like ammonia, nitrite, and nitrate, or is this constant? Even after doing a test I feel no wiser and yes Im still a newbie, but i keep seeing the importance of knowing my KH and GH.

Someone please help.

 

[Rocky998]

KH and GH directly affect PH and the fish's health.
Some fish like high PH/GH while other fish like a low GH/PH.
GH is the water's hardness so it measures how many minerals there are in the water per X amount.
PH measures how acidic the water is and and KH is a "trash can" for the PH. The higher the KH the harder it is to change the PH and vice versa

 

[Naughts]

GH is very important as some fish evolved in soft water and some in hard water. If you keep fish that match your water they will be healthier and live longer.
KH is linked but not as important.

Understanding water hardness

Water hardness — not the most exciting of subjects to try and fully understand. The extensive amount of terminology makes the subject seem endless and confusing in equal measure.

www.practicalfishkeeping.co.uk

 

[Byron]

That is a good summary in the post above. It may not answer your second question that well though, so I'll comment on "does this change?"

Yes and no, usually. We ask about the GH, KH and pH (all three are connected) of the source water, usually tap water which will be municipal or sometimes a private well. This is crucial, because the relationship of the three parameters is connected and as the article notes you cannot usually change one without considering the whole "pie." The higher the GH and KH, the less likely the pH will change, as noted in the article. The lower the GH and KH, the more possibility that the pH may lower, but it all depends upon the initial relationship and levels.

Normally, the GH and KH will remain close to the initial levels in the source water. Adding calcareous rock, substrate, coral, and shells will tend to increase the GH or KH or pH. I must here again mention that the initial values of all three determine the effect. In reverse, as the article noted, adding organics such as leaves, wood, peat and the natural waste organics will work to lower these values, but again the extent depends upon the initial relationships.

Regular (once a week) substantial (50-70%) partial water changes go a long way in maintaining stability.