KH, PH, GH Confusion

[tomm10]

I'm a lttle confused about my water chemistry at the moment.

As I understand it, in very simplified form, ph refers to the acidity of the water. 7.0 being neutral with lower being acidic and higher being alkaline.

kh and gh refer to the hardness of the water. GH refers to the total amount of salts or minerals in the water (including metals which can affect total hardness). Kh refers only to the amount of carbon in the water.

Now, I know KH acts as a buffer to protect the water from sudden changes in ph. A higher KH should mean its harder to get a ph drop in your water. A lower KH would mean you're more susceptible to a crash. A low KH is generally coupled with a low ph and vise versa.

This is what I THINK I know in generalized terms.

The problem is, I finally got a KH test kit and became confused. My tank tests for 30 mg/l with both GH and KH. This is pretty low so my thought would be that I should have a pretty low ph, right? Wrong. My ph is 7.2.

Its worth noting that before I started doing all my water changes with cold water that ran for at least 3-5 minutes before being collected my tanks tested for 50 mg/l GH.

The question is, how can I have such a low kh and gh yet still have slightly alkaline water (not that I'm complaining! 7.2 is ducky with me)?

Also, I am planning on adding the little Hagen CO2 kit to the 29 gallon tank once I put the 55w PC on. Since this would introduce more carbon to the water, would this increase my buffer? If not, how would it affect my water.

I never was this bad at chemistry in high school
:shake:

Tom

 

[tomm10]

Nothing like replying to your own threads!

I re-read RTR's Article on Tom's Place again (a GREAT explaination by the way its just such a complicated subject for my little brain that I have to keep reading it to let it sink in ) and think I understand some things better.

I believe that since I have well water and take great pains to make sure it spends as little time in the plumbing of my house as possible, it is extremely well filtered and pure. This leads to the low KH and GH and a pH very close to neutral at 7.2.

Now I think I understand that adding C02 will cause a lowering of my pH so the question is, by how much?

Should I attempt to slighlty buffer my water by adding some carbonate source to my filter before I introduce C02? Does anyone have a material to recommend?

This is for a 29G tank by the way.

Tom

 

[RTR]

Generally it is suggested that the KH be at least 3-5 degrees when CO2 is being added, to provide some stability and to avoid very low pH.

http://www.sfbaaps.com/reference/table_01.shtml

The table on the SFAAPS site will give you info about how much CO2 will depress pH at varying KHs.

I usually suggest aragonite or coral rubble in a mesh bag in a filter to boost GH/KH. But with the warning that this is not fast (which is a benefit to me) and may require quantity adjustment periodically and/or rinsing away old biofilms which may slow solution down even more.

 

[tomm10]

Thanks, RTR. I think I actually had my test results a little screwed up. I believe my KH was actually at 60 ppm wich would me about 3.35 degrees of hardness or so. Still on the low side for KH.

I'm still a week (easily) away from adding C02 so I'm not worried about the time neccessary to increase the buffer. I have no idea what level to start with. A tbsn of coral rubble maybe? I also wouldn't have any idea of how long I should wait for results before increasing the dosage.

What about starting off with two tbsns of coral rubble in a mesh bag on my hob filter. I'll wait a week for results and then add or subtract a little from there. does this sound right?

Thanks for the help!

Tom