More newbie questions if you can stand it.

[dogdoc]

This question is actually about the pH/GH/KH relationship.

I have fairly good quality tapwater at home. It comes with a pH of 7-7.2 and even after 24 hours it generally stays at this level. It is fairly soft water with KH and GH both about 3 degrees ( around 50-55 ppm?).

What I find odd is that my pH in the tank seems to slowly but steadily rise to between 7.2 and 7.6 between water changes.

I do about a 30% change about every 5 days. Ammonia is 0. Nitrite 0. Nitrate 5. The only things in the tank besides fish are a piece of driftwood, aquarium gravel, some anacharis plants, and a piece of fake (resin) coral.

 

[JNevaril]

science time.

I did some research, because your question intrigued me.

Check out this website, it explains A LOT about water chemistry in the aquarium...

http://www.aquariumsite.com/freshwater/chemistry.php


....yoink........from fishindex.com....

"If there is a greater concentration of hydrogen ions [H+] vs. [OH-] (hydroxide ion concentration), the the water is acidic and has a pH lower than 7. When [H+] is lower than [OH-], the water is basic and has a pH higher than 7. When [H+] = [OH-], the pH is neutral, or 7, exactly.

So, pH is simply the inverse log of the hydrogen ion concentration, denoted as:

pH = -log[H+]

Once you begin to consider Lewis Acids/Bases, pH becomes a little more complex, but the above is more than enough for most aquarists. The most important thing to remember is that you should never allow the pH to change rapidly in your tank -- limit any changes to .1 increments, if possible. Since pH is a logarithmic function, you can see that changing pH by a degree in either direction is actually a 10x change in relative acidity.

It's OK to manage by the numbers.

KH is Carbonate Hardness or Alkalinity and consists primarily of bicarbonate (HCO3-) (and other buffers).

Unless you're doing something special with your tank (biotope, peat, Reverse Osmosis, etc.), your KH should be around 5.

GH is General Hardness and consists specifically of the amount of calcium (Ca+2) and magnesium (Mg+2) in the water and generally does not directly affect pH. If you are manipulating GH by adding calcium, lime, or magnesium to your tank in some inorganic form, you may increase the KH by adding carbonate resources to the water column. As calcium carbonate (hard white precipitate - CaCO3) forms on your hood and elsewhere, your GH and KH will drop, since both calcium and carbonate are being removed from the water column. The subtle alterations in GH that affect KH, in turn indirectly affect pH because of the KH changes.

Unless you're doing something special with your tank (bioptope, cichlids, Reverse Osmosis, breeding, etc.), your GH will be determined by whatever calcium and magnesium you've got in your tap water. GH is also called "permanent hardness." If you have hard water, you generally know it, since you use a water softener in your house and will may also note the accumulation of CaCO3 on your water faucets and elsewhere (besides the basic water chemistry test).

Water that has a low GH is called "soft water." Water that has a high GH is called "hard water." Similarly, because of the relationship between GH and KH, hard water tends to have higher alkalinity (KH).

KH is your primary defense against the build-up of acidic materials in the tank, include nitric acid from nitrate accumulation (the end-product of the ammonia produced by your fish) and carbonic acid from dissolved CO2 from the atmosphere, respiration, or direct injection. So, KH prevents sudden drops in pH. The higher the KH, the higher (& more stable) the pH. The lower the KH, the lower (and more unstable) the pH.

If you allow the nitrates from processed fish waste to build up in your tank to very high levels in the presence of low KH, you can experience a tank pH crash. This is why (among other reasons) that it's a good idea to perform regular water changes. Also, if you inject CO2 in the presence of an insufficient KH (alkalinity), you can cause a pH crash. Rapid, wide swings in pH will stress or kill your fish.

There is some useful info about GH, KH, and pH in this older thread and elsewhere in the forum:
KH vs. GH - what's the difference?

This is just a quick overview, but it should address the question. Once again, it's OK to manage by the numbers. Pay particular attention to your KH, while developing an appreciation for and understanding of the interaction among GH, KH, and pH.

Note that if you use a Reverse Osmosis filter, it will strip all the hardness and alkalinity out of the water, so you must resupplement with essential buffering and electrolytes in order to prepare the water for use in your tank.

Also, there is some confusion around the words alkalinity and alkaline. Alkalinity is the total pH buffering capacity of the water (KH). However, Alkaline solutions are Bases and have a higher [OH-]. So, it's best not to confuse the two."

 

[dogdoc]

I guess that I understand all of that pretty well. Takes me back to all of my chemistry courses in school.

What seems counter-intuitive to me, is that I have fairly soft water (if not very soft) and yet my pH seems to behave as I would think hard water would. Meaning I would expect to have problems with the pH dropping or being unstable with soft water like mine. Instead, it seems to be fairly stable and if anything pH creeps up. Doesn't do it drastically, but if I test pH regularly between changes I do notice it.

I guess that my underlying reason for asking this question is that my daughter loves her Mollys. And they have been the hardest to keep alive. My research has indicated that Mollys like harder, more alkaline water. But at the same time, they are in the same tank as neon tetras, a phantom tetra, and a black skirt tetra which all like the soft, acidic water.

I guess I was wondering if it is possible to make the water a little harder without causing my pH to be 8. Maybe this would improve my luck with Molly's and not harm my tetras. (I call them mine, but they are actually my daughter's). I don't know, maybe they just aren't compatible enough to live together, or else I'm doing something wrong.

 

[FroggyFox]

Practically...you're right. I have NO idea why your pH would be going up from the point it is 24 hours outside the tap. You could do a little experiment. Take a cup of water at the same time you do a water change and set it by the tank...test it and see if it too continues to raise in pH over the course of the week past that 24 hour mark. Some tank decorations, substrates etc have been known to screw with pH levels. crushed coral was one...I read coral, but then realized you said it was resin not real coral. So the cup of water outside the tank would be your "control" and if the water in the tank changes more than the water in the cup you know there's something IN the tank that is causing the fluxuations rather than your water behaving wierdly.

Livebearers and mollies do best in harder/higher pH water...tetras do better with softer/lower pH water...but ya know what...they all do just fine in water with a stable pH kh gh, no matter what that number is. If you get into breeding and what not you might want to get into that some more...but I would think right now you should see what you can do to figure out whats making it move and keeping it stable.

btw, my understanding of this is kinda foggy, I didn't even read what Jnevaril posted because I never did incredibly well in chemistry, just enough to get by BUT I do think that just because you have soft water doesn't mean it has to be a low pH...it just means that it has a lower buffering capacity so the water doesn't have the capacity to hold a steady pH. I believe if you raise the hardness of the water your pH will be more stable...but you might want to read some more about that. That was just the understanding I had.

 

[dogdoc]

Maybe I'm just cursed with Mollys.