# Struggling to understand the role of gh



## cwlodarczyk (Sep 18, 2005)

I'm relatively new to keeping aquaria and plants and while I understand the importance of ph, fert routines, etc. and am starting to "get" kh, I'm still not grasping what the role of gh is.

Adding even more to my confusion is that I really never see any discussion about very high gh. Most of the posts I've come across are questions of how to raise to minimal levels. In my case gh tests at 17 from the tap and 18 in my tank.

So what are we really talking about and what does it mean for what kind of plants/fish that I'll have the most success with?



A couple of notes: I used the AP test kit for my results. I don't know the kh (need to pick up a kit today). I'm in Orange Co., CA - if anyone is close by maybe you can tell me what these levels mean for your tanks.


-Carl


----------



## ringram (Jan 10, 2005)

GH = general hardness, which is a measure of the dissolved solids(metals, essentially) whereas KH = carbonate hardness(measure of the buffering capacity of the water). 
When people say that their water is hard, they are usually talking about GH.
Hope this helps.
-Ryan


----------



## cwlodarczyk (Sep 18, 2005)

ringram said:


> GH = general hardness, which is a measure of the dissolved solids(metals, essentially)


I understand what it IS, but I'm not quite grasping what it DOES. How does the hardness affect plant health, fish health, etc? What are the concerns for very high / very low hardness? In short, why does it matter?


----------



## TWood (Dec 9, 2004)

The link to the page I was going to go to is broken...But google GH and water hardness and some pages will come up.

Basically GH is a measure of the calcium (Ca) and magnesium (Mg) in the water, plus some other minor elements. Our water is GH=24 (AP test kit) and an electronic TDS meter reads 420ppm. Multiply 24 times 17.9 to convert degrees to ppm and I get 430 ppm - within the margin of error and indicating that the TDS (total dissolved solids) is mostly Ca and Mg.

What does that mean as far as plants? I couldn't grow what I wanted in that water so I went with an RO unit so I could control GH, KH and TDS. I've seen posts by Tom Barr that assert that high Ca will interfere with nutrient uptake. It sure seemed to affect CO2 availability, and Barr's advice, as usual, was to keep cranking it up. That affected my fish, so I went the RO route. But if the GH is too low, then there's not enough Ca and Mg to grow, so a happy medium is best.

Sidenote: The titration test kits are looking for Ca and Mg. Our house has a salt-based water softener that replaces them with sodium chloride. The TDS meter would still read 420, but the GH was 1 because the test kit doesn't react to salt. So it's important to know what the test kits are actually measuring. The TDS meter is actually a conductivity meter with a built-in conversion factor.

TW

Edit: As far as fish go, most can adapt to any level of hardness, within reason, but some need special parameters to breed.


----------



## Phil Edwards (Jan 22, 2004)

Many many many plants will grow in a high GH. Florida lakes and rivers are sourced by streams and springs that come from limestone rich areas that make the water hard. All of those extra dissolved solids will only benefit your plant as they're things plants need anyway. Think of GH as extra Calcium and Magnesium supplimentation on top of what you do already.


Regards,
Phil


----------



## Laith (Sep 4, 2004)

I'm growing plants in a GH of of 18 and KH of 15.5 and most of the GH around here is Calcium.

I used to use RO water then gave it a try without. Never really noticed a difference except that I find that I need to add quite a bit more Fe and traces than before.


----------



## TWood (Dec 9, 2004)

Our water supply is from groundwater wells and with minimal treatment. At this time of year the local waterways are all groundwater fed. These waterways are almost totally vacant of plantlife. If it were possible, it seems that -something- would have evolved to grow in the water here, particularly in an area where water is scarce. Annual rainfall is only 22 inches. So at some point, even nature gave up on this water. An aquarium is just easier to manage at more reasonable GH levels. 

TW


----------

