Relationship between PH and KH?

Hi everyone! Here is my question...if you know the KH of a given solution of water, can you roughly estimate the PH of that sample? I am trying to devise a new salt mix for my planted aquariums...the current mix creates water with 7 dKH and a PH of around 8, and some of my plants are not doing well in that mix (likely because almost all the CO2 getting dissolved into these highly alkaline tanks is getting converted into bicarbonates that the plants are unable to use); thus, I am trying to determine how much (if any) KH I can add (to increase stability in the tank) to my very soft (less than 1 GH and KH!) tap water without pushing the PH to such unreasonably high levels. Thanks

 

Hi everyone! Here is my question...if you know the KH of a given solution of water, can you roughly estimate the PH of that sample?

Perhaps if your water wasn't being influenced by anything else one could do this. But, there are several acids, like carbonic acid from CO2, that can lower pH and complicate things.

I am trying to devise a new salt mix for my planted aquariums...the current mix creates water with 7 dKH and a PH of around 8, and some of my plants are not doing well in that mix (likely because almost all the CO2 getting dissolved into these highly alkaline tanks is getting converted into bicarbonates that the plants are unable to use);

Also, several nutrients are less available to plants in alkaline conditions.

thus, I am trying to determine how much (if any) KH I can add (to increase stability in the tank) to my very soft (less than 1 GH and KH!) tap water without pushing the PH to such unreasonably high levels. Thanks

I don't know the answer to this one, but there are already products on the market (like Seachem Equilibrium and Alkaline Buffer) that do this. Might it be easier to just buy a product than make your own?

 

Hi everyone! Here is my question...if you know the KH of a given solution of water, can you roughly estimate the PH of that sample?

Really good question.
I've read that pH doesn't really move/lower until KH is 0.
Yet I have been experiencing no significant change in pH with a 0 KH for weeks (months?) now.
I'd have to say no. One can't determine the other. Yet one can affect the other.

 

Hi everyone! Here is my question...if you know the KH of a given solution of water, can you roughly estimate the PH of that sample? I am trying to devise a new salt mix for my planted aquariums...the current mix creates water with 7 dKH and a PH of around 8, and some of my plants are not doing well in that mix (likely because almost all the CO2 getting dissolved into these highly alkaline tanks is getting converted into bicarbonates that the plants are unable to use); thus, I am trying to determine how much (if any) KH I can add (to increase stability in the tank) to my very soft (less than 1 GH and KH!) tap water without pushing the PH to such unreasonably high levels. Thanks

I’m not certain it’s the ph that is the culprit with your plants. My tanks have always had ph between 8.0-8.2 and the plants did remarkably well. That said, my plants have always been low to moderate light, not high light.

What plant products are you using? I’d look at those. Better to have the higher KH, thus stable PH like you’re doing.

 

I’m not certain it’s the ph that is the culprit with your plants. My tanks have always had ph between 8.0-8.2 and the plants did remarkably well. That said, my plants have always been low to moderate light, not high light.

What plant products are you using? I’d look at those. Better to have the higher KH, thus stable PH like you’re doing.

The plants I am primarily having issues with are Ludwigia 'super red mini' and Rotala rotundifolia. The hornwort and corkscrew vals (both of which can use bicarbonates) are growing furiously in my tanks (interestingly, the KH of the 5 gallon went down several degrees over the past week, evidently because the hornwort was using bicarbonates furiously...the PH was still 8, though). The cryptocoryne wendtii 'green' is doing only ok in both tanks (it's growing but looks a little leggy). The dwarf water lilies are growing fine, but they might be using energy stored up from the tuber. While I would like a little KH if it isn't going to send the PH shooting up to 8, I have kept a variety of 0 kh blackwater tanks (including my Betta dimidiata tanks I have now) and it has been surprisingly hard to get such tanks to drop below a PH in the high 5's/low 6's (and they don't seem inclined to climb much higher than that either), so I think I could get away with little to no added KH assuming I don't put hard water fish/plants in those tanks (I was still going to add calcium chloride, potassium chloride, and epsom salts to the water to provide calcium, potassium, and magnesium if I go that route...just no bicarbonates). I did use thrive C and a double dose of excel (it started as a half dose but was slowly increased over the first few months of the tank's existence) in my 10 gallon in the past but ran into similar issues with the non-val plants I had then (tiger lotus, ludwigia 'rubin', dwarf sag, and echinodorus 'miracle'). The 5 gallon is dirted and not very old, so I don't think it is a nutrient deficiency in that tank.

Really good question.
I've read that pH doesn't really move/lower until KH is 0.
Yet I have been experiencing no significant change in pH with a 0 KH for weeks (months?) now.
I'd have to say no. One can't determine the other. Yet one can affect the other.

I've kept a number of very soft blackwater tanks over the roughly 10 years I have been in the hobby and have likewise not had issues with PH fluctuations with them...even if I deliberately added acids to 0 KH, low TDS water (which, I should add, did not have fish at the time), it still usually climbed back to the high 5's/low 6's within a day. I'm glad to see that this was not a fluke.

Perhaps if your water wasn't being influenced by anything else one could do this. But, there are several acids, like carbonic acid from CO2, that can lower pH and complicate things.

Also, several nutrients are less available to plants in alkaline conditions.

I don't know the answer to this one, but there are already products on the market (like Seachem Equilibrium and Alkaline Buffer) that do this. Might it be easier to just buy a product than make your own?

I COULD buy one of those buffers...but I'm a control freak!

On a more serious note, though, those buffers are not particularly cheap. I have no aversion to mixing the individual salts myself to save some money. I mix the salts in a bottle of water and dispense a certain amount of that mixture into new WC water to add the desired amount of minerals.