# GH, KH, CO2 & Plants



## rjordan393 (Nov 23, 2012)

Is there an ideal range for GH and KH for plants when injecting CO2? I been keeping my GH at 8 dGH and my KH at 4 dKH. I use Seachems Equalibrium to raise GH and their Alkaline Buffer to raise KH. Should I adjust one or both parameters?


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## Diana K (Dec 20, 2007)

Set the GH to keep the livestock happy. Soft water fish = lower GH. Hard water fish = higher GH. Almost all aquarium plants will adjust to almost any level of GH that works for fish. Zero is not good; both fish and plants need calcium and magnesium. There are a few specialty plants that really do require very low mineral levels, and acidic water. Not very many, though. 

I usually try to keep the KH roughly equal to the GH. I am trying to match (sort of) what there is in nature:
If the water is soft (low GH) then it is often acidic, or neutral. Low KH. 
If the water is hard (high GH) then it is often alkaline. High KH. 
Most of the time in nature the minerals are from dissolved limestone or related minerals. Limestone and its relatives are almost pure calcium carbonate or magnesium carbonate, with a small amount of almost everything else. Some limestones dissolve easier than others, but almost all will add roughly equal amounts of calcium or magnesium (or a blend) and carbonate. 
Calcium and magnesium = GH
Carbonate = KH. 

Fish do not mind the pH swings that happen as the plants use the CO2 through the day. The mineral level needs to be stable, though. 

I use Equilibrium for GH and baking soda for KH. Read the label on most products that raise the KH, no matter how they word it. Many are sodium bicarbonate. In other words, baking soda. Some are not, and if you like the product you are using, keep on using it. Just suggesting that if that particular one is simply a fancy way of selling baking soda... 

When you are growing plants using CO2 you are expecting them to grow faster, and this means they will use more fertilizer, minerals and so on. 
Do not let the GH get too low, do not let the plants starve for calcium or magnesium. If you find that 8dGH is stable for you, then go for it. 

It is higher than most of my tanks run, but I am not using a lot of CO2. Mostly Excel, so the plants do not remove the Ca or Mg faster than I am adding it (which is not very fast).


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## Yo-han (Oct 15, 2010)

Perfect values, suitable for almost all fish and plant. Unless you want to try very specific plants or fish, keep them that way


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## rjordan393 (Nov 23, 2012)

Thanks,
Now I am concentrating on fine tuning the fertilizer dosage based on what the plants take up. I have a base dose set up after my water change and then a maintenance dose after that. On the day of my next water change, I will test the NO3, PO4, K and FE before and after the water change to come up with how much of each needs to be adjusted.


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