mos90

from what ive been told and read in a planted tank with c02 inj, kh isnt an important factor. mine is about 2. i use a ph contoller and keep my ph around 6.4 and 20-25pmm c02. i know if i raise my kh i can maintain the same amount of c02 at a higher ph.

i know many people that dont mess with kh if they use a ph contoller and c02, then just adjust levels of c02 by lowering ph.

my question is , why not leave kh alone even if its at 1 or 2 and just lower ph to control c02 levels?

i guess 1 reason i can think of would be if you are shooting for a target ph of like 7.5 with optimal c02 levels. then kh would need to be much higher then 1or 2.

any other reasons?

bosmahe1

I wouldn't mess with your kh at all. Use a drop checker with 4 kdh water in it to adjust co2 to 30 ppm (green). Then look at the ph on the controller and adjust the range around that particular ph.

mos90

thats exactly what im doing. but is there such a thing as kh being to low and can it harm plants or limit growth?

Seattle_Aquarist

Hi mos90,

I have extremely soft water here in Seattle, typically less than 2.0 KH. I have certain plant types (usually the faster growing stem plants) that experience deficiencies that I attribute to the soft water (lack of minerals).

Diana K

Is the GH also low? Calcium or magnesium deficiency?
These are not the same as KH (Carbonates) but low KH and low GH are often found in the same water. Easy to compensate for.

I have some tanks where the substrate has removed the KH from the water. Fish and plants are OK as long as there is a source of carbon. This substrate does not touch GH.

Some plants can use KH as a source of carbon. Usually these are plants from hard water lakes and streams, and also need higher Ca, Mg and other minerals. Watch for deficiencies in these, if the GH is also low.

Nitrifying bacteria do not do so well in acidic water (pH about 6). I do not know if it is actually the pH, or the low mineral content (KH, or GH) that often accompanies the acidic water.
In a heavily planted tank the nitrifying bacteria are not much of an issue, plants are the nitrogen sponges, but do not remove so many plants all at once, thinking the nitrifying bacteria will take over. There might not be enough of a population to handle all the fish waste.

Philosophos

Presuming you fert, low KH doesn't cause issues with most species of plant. Low KH and CO2 still keeps people at 6pH and up quite often, which is great for many plants. There are a few species that will prefer harder water, but these tend to be the exception.

In my opinion, pH controllers aren't all that great of a thing. It's consistent CO2 that you're after for plants, not consistent pH. For fish, you want consistent KH; consistent pH from CO2 isn't a big deal. Over 95% of the CO2 you pump into your tank isn't going to turn into plant, and I can promise your concentration of H+ is going to vary more than +/- 2.5% without even accounting for calibration and localized variances. I know it's something you probably don't want to hear after spending the money, but would you want to keep it if it's making it more difficult for you to achieve non-limiting CO2 levels?

-Philosophos