Low GH/KH, high PH??

[bynna]

I got the hagen master kit today and just tested the hardness of my tap water. The result is really confused:

GH: 40mg/L = 2.23 degree
KH: 45mg/L = 2.51 degree
PH: 7.9

In another word, I have a very soft water with high PH. As far as what I have learned, high PH is always associated with high KH/GH. Any idea why I'm getting this type of water?

I'm starting a 10G planted low tech tank (2*15W spiral CFL, NO co2 planned). Based on the tap water I have, is there any type of plants I should avoid? Or should I do something do alter the GH/KH? Cause I've heard that KH should be maintained at a certain level in order to buffer PH. BTW, I'm planning to throw a Malaysian driftwood into the tank, hopefully it'll bring the PH down a bit. Thanks.

[Danni]

I have similar water... pH out of the tap is 7.4, GH is 4 and KH is 3. In the tank the pH drops to 6.6 or lower if I let it. GH is 3 and KH 2. I have several pieces of driftwood which may account for the pH dropping like that. I have included crushed coral in my filter to try to buffer the water somewhat to hold a steady pH...seems to be working as it hasn't dropped below 6.8 and today is hovering around 7.2. KH is the same at 2 and but GH has gone back to 4. I have plants for low light and all of them seem to be doing just fine. I have seen growth on all of them. You should be okay to grow what you want with the driftwood in there.

[angrycow]

the city raise the ph of the water to control rusting, scaling and other ings within the municipal system.  Let it sit a little while and it drops to neutral or just below. 

[bynna]

Thanks Danni. I just bought a bag of aragonite today. Planning to put them into a small brackish tank containing 2 mollies and a smaller tank with one applesnail in it. But I'm still worried about one thing: if the hardness is increased by the aragonite, the PH will be increased accordingly. This is something I wanna avoid, cause my PH is already 7.8. I don't want it  to be higher. But I don't know how to stable the PH at the same time.

Angrycow: Tested a tap water sample which has been sit for about 2 weeks. Surprisingly the PH hasn't dropped even a bit, it's still 7.8.   

[kennyman]

Read up on Diana Walstads forum on "Aquarium Plant Central". She had a forum called "El Natural" her natural tank system is based on high ph, medium/low light aquariums. My tank is run on the same principals as she promotes and I find it extremely easy to maintain. There are preferred pant lists, water parameters and lighting listed there.

Also aragonite will stop buffing when there are no acids to break it down. Since aragonite is less stable then crushed coral it buffers to around 8.0Ph rather then the mid 7's of crushed coral. Since your ph is high despite low Kh you probably lack sufficient acids to really activate the aragonite.

You could always use baking soda and epsom salts to raise hardness at water change time. These are the primary compounds that make hard water hard and will allow you to set you Kh exactly where you want it.

[bynna]

Kennyman, thanks for your information. I'm reading the articles from the web site you recommended. It's full of knowledges which is exactly what I've always being looking for.

So for now, I'm going to put aragonite only into the applesnail tank. Because I think what the snail really need is GH instead of KH. Another thing I tried is putting a pill of Calcium which is the supplement sold at regular pharmacies into the tank. Only a few hours after, my GH bounced to 80ppm, and KH 100ppm. Don't know if anybody else has ever tried this way before.