GH is General Hardness. KH is Carbonate (aka Temporary) Hardness. dh is "degrees of hardness", the units by which both of these are measured.
Hardness is an expression for various minerals being dissolved in water. The modern way that scientists discuss harness measurements is in milligrams/litre (mg/l) just like many of our other dissolved things we discuss here in fishkeeping. Since the total amounts of dissolved substances we discuss are usually very low, we can also discuss them in parts per million (ppm) although technically speaking mg/l is more correct than ppm because mg/l refers correctly to solids in liquids, whereas ppm technically would be solids in solids or liquids in liquids.
There are about five supposedly obsolete "degree" scales traditionally used to express hardness measurements: Clark(English) degrees, French degrees, American degrees, degrees of General Hardness (dGH) and finally, Deutsche Härte (German hardness) (dH), this last being the one most commonly still used by aquarium KH kits. One german degree is equal to 17.9ppm or mg/l of hardness. This conversion number is often useful in various situations such as talking with a local water authority who might use ppm instead of german degrees.
So now you have the tools to look more closely at your expression of "dh" and understand where it is coming from.
OK, so Carbonate Hardness is not "good" or "bad" overall, but a very common situation, like yours, is to want to raise it (raise KH to a higher value) because when it is very low it means your water has very little "buffering" capacity and is very susceptible to large pH changes, which are usually not desirable in an aquarium. KH and pH generally work in tandem in the world of aquariums and there are both fish and plants that, in their natural habitat, prefer soft & acid water (low KH and low pH) and other fish and plants which prefer hard & basic water (high KH and high pH), so this is yet another area that may need to be considered by both the fishkeeper and the planted tank enthusiast.
One reason I'm getting so detailed here is to hopefully give you a picture of some of the complicated nature of what you've asked about and help you understand that easy answers, although you may receive plenty of them, sometimes can hide the overall complexity. In the end the actions you take will probably be fairly simple but I just think it helps to have some larger picture stuff. MW has already hinted that the two actions we take for raising KH (&pH) are corals and baking soda. But more important than -how- we do it, is -whether- we should do it.
I feel I'm good at explaining -how- to raise KH (via baking soda or corals and when to use which) and I can contribute to a conversation about -whether- a particular fishkeeper should choose to do it but I'm not at all the best or most experienced at the -whether- part, because the very best people at that are those that have had lots and lots of experiences trying it and failing or succeeding! So.... my own choice would be to slow down a bit here, have a longer conversation, waiting for other experts to add their voices.
Another simple piece of accepted lore, I believe, which I can safely leave you with is that generally we recommend the "corals" methods for "operational" tanks with fish. The "baking soda" method I usually like to only recommend as a method of raising KH during a -fishless- cycle (the reason being that baking soda acts immediately, which is good, but is shorter lived and must be looked after and replenished fairly soon.) This is not to say that the "slower startup" but "longer acting" coral methods can not be effectively used during fishless, as I think they can, but just that often people end up using the two types of methods in the ways I've described.
~~waterdrop~~
/www.petfish.net/articles/pix/arts2/ph_kh_co2.gif, but ive got dh which, i think is wrong the type
, lol, so am i right in thinking that dh is to low to be measured correctly and that ive got to add stuff to one of my filter baskets to increase to kh?
