PH Issues in biotype

[central tanks]

Well having it as a planted tank could make it not a biotype, nut ill post any ways. Im using RO water and remineralizing it with Equilibrium. With this my water is as follows-
PH-6.8
dKH - 0
dGH - 3
TDS - 160

My issue is getting the KH raised up for the plants, If i remember correctly they need KH to survive. I have some Alkaline KH Buffer but it raises my PH to about 8. I can dose then drain half my water and e fill with RO and come out with 3dkh but ph is still at 7.8. Is there a way to raise my KH to around 3dkh without raising my PH?

 

[central tanks]

side bit, all this dosing and drining is in a 10 gallon water mixing container not the tank. Ill be keeping Apistogramma cacatuoides

 

[boofeng]

You have great water for keeping apistos!

I don't know how to raise KH without raising pH... I think you have to choose a mix of chemicals that buffer at the pH you want, maybe like Seachem Discus Buffer, which buffers at around 6.5. Sodium bicarbonate is often suggested, but I think how much it affects pH depends on your water to begin with. Let's wait for the chemists here to chip in.

My approach is to instead search for plants which thrive in low pH and zero KH. I've come across planted tank hobbyists who run zero KH and their plants do well (though on that thread, 90% of people were asking him to go for at least KH 1-2). Locally, lots of apisto hobbyists keep them in zero KH, and they grow java fern, cabomba, ceratopteris, potamogeton gayii, and various crypts.

A more recent approach is here. His rationale for keeping plants at zero KH is quite interesting:

My target plants come for very soft acidic waters with near-zero hardness and pH in the 4.0-5.5 range. At this pH virtually all inorganic carbon is present as CO2 with no bicarbonate. This favours my target plants that evolved to exclusively use CO2 and disfavours the many plants, and perhaps algae, that rely on bicarbonate as an extra source of carbon.

 

[central tanks]

Thanks for all the info! Iv decided to just use the 0kh water and see how my plants react. I'm using mostly crypt plants with a back row of temple plants, and some Red Tigard Lotus. If the plants start melting due to low kh I'll just have to get a second tank for a actual biotype and use the planted tank for something else lol.

 

[dw1305]

Hi all,

My issue is getting the KH raised up for the plants, If i remember correctly they need KH to survive.

It is like @boofeng says, it depends on the plants, but plants from soft water don't need any dKH to grow.

I have some Alkaline KH Buffer but it raises my PH to about 8. I can dose then drain half my water and e fill with RO and come out with 3dkh but ph is still at 7.8. Is there a way to raise my KH to around 3dkh without raising my PH?

No, not really.

I won't do all the chemistry, but basically carbonates are insoluble in pure water, but soluble in weak acids. RO is close to pure H2O, but CO2 will dissolve into, and a small portion of that CO2 will become carbonic acid H2CO3, which will lower pH of the water. In a system with carbonates (CO3) present (so any dKH), we have a buffered system and H2CO3 ~ HCO3- ~ CO3 are in equilibrium with a pH value of pH8 at 400ppm of atmospheric CO2.

Thanks for all the info! Iv decided to just use the 0kh water and see how my plants react. I'm using mostly crypt plants with a back row of temple plants, and some Red Tigard Lotus. If the plants start melting due to low kh I'll just have to get a second tank for a actual biotype and use the planted tank for something else lol.

Hygrophila corymbosa doesn't like very soft water, but is all right otherwise. I can't keep C. crispulata "Balansae", but all the other Cryptocoryne spp. I've tried have been fine.

I'd highly recommend Cryptocoyne x willisii as a small Crypt for a soft water aquarium.

cheers Darrel