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I just remembered I wanted to post about this:
I was doing water changes and tests over the weekend and noticed that the pH in my 29 gal. was down to ~6 while my 36 gal. and tap water are both at 7.2. The weird thing is that everything in the 29 is fake (plants and decor, all have been in there for over a year) so I have no idea what would be causing such a drop.
I did the water change after I tested the water, so I imagine the pH would've gone back up a little, but I'll try to remember to test it tonight or tomorrow to see where it is now. I'm not really that worried about things right now as all the fish seem to be doing fine, but I just want to make sure this isn't a warning sign of something to come...

Oh, the other parameters were (before the water change):
Ammonia: 0
Nitrite: 0
Nitrate: 10
Temp: ~80 (cheap heater)
dH: 7

Thanks!

Josh,

I presume that when you measured your hardness as dH: 7 that you were measuring General Hardness.

Water hardness is of interest to aquarists for two reasons: to provide the proper environment for the fish and to help stabilize the pH in the aquarium. There are two types of water hardness: general hardness (GH) and carbonate hardness (KH). A third term commonly used is total hardness which is a combination of GH and KH. Since it is important to know both the GH and KH, the use of total hardness can be misleading and should be avoided.

GENERAL HARDNESS
General hardness is primarily the measure of calcium (Ca++) and magnesium (Mg++) ions in the water. Other ions can contribute to GH but their effects are usually insignificant and the other ions are difficult to measure. GH will not directly affect pH although "hard" water is generally alkaline due to some interaction of GH and KH.
GH is commonly expressed in parts per million (ppm) of calcium carbonate (CaCO3), degrees hardness (dH) or, more properly, the molar concentration of CaCO3. One German degree hardness (dH) is 10 mg of calcium oxide (CaO) per liter. In the U.S., hardness is usually measured in ppm of CaCO3. A German dH is 17.8 ppm CaCO3. A molar concentration of 1 milliequivalent per liter (mEq/l) = 2.8 dH = 50 ppm. Note that most test kits give the hardness in units of CaCO3; this means the hardness is equivalent to that much CaCO3 in water but does not mean it actually came from CaCO3. Water hardness follows these guidelines:
0 - 4 dH, 0 - 70 ppm : very soft
4 - 8 dH, 70 - 140 ppm : soft
8 - 12 dH, 140 - 210 ppm : medium hard
12 - 18 dH, 210 - 320 ppm : fairly hard
18 - 30 dH, 320 - 530 ppm : hard
higher : liquid rock (Lake Malawi and Los Angeles, CA)
General hardness is the more important of the two in biological processes. When a fish or plant is said to prefer "hard" or "soft" water, this is referring to GH. Incorrect GH will affect the transfer of nutrients and waste products through cell membranes and can affect egg fertility, proper functioning of internal organs such as kidneys and growth. Within reason, most fish and plants can successfully adapt to local GH conditions, although breeding may be impaired.

CARBONATE HARDNESS
Carbonate hardness (KH) is the measure of bicarbonate (HCO3-) and carbonate (CO3--) ions in the water. In freshwater aquariums of neutral pH, bicarbonate ions predominate and in saltwater aquariums, carbonate ions begin to play a role. Alkalinity is the measure of the total acid binding capacity (all the anions which can bind with free H+) but is comprised mostly of carbonate hardness in freshwater systems. Thus, in practical freshwater usage, the terms carboante hardness, acid binding, acid buffering capacity and alkalinity are used interchangeably. In an aquarium, KH acts as a chemical buffering agent, helping to stabilize pH. KH is generaly referred to in degrees hardness and is expressed in CaCO3 equivalents just like GH.
In simple terms, pH is determined by the negative log of the concentration of free hydrogen ions (H+) in the water. If you add a strong acid such as nitric acid to water, it completely dissociates into hydrogen ions (H+) and its "conjugate base" or "salt", NO3- or nitrate. The hydrogen ions freed in the reaction then increase the concentration of hydrogen ions and reduce the pH. Since nitric acid is the end product of the nitrogen cycle, this explains why aquarium pH tends to decrease and nitrates tend to increase over time.
When the aquarium has some carbonate buffering in it, the bicarbonate ions will combine with the excess hydrogen ions to form carbonic acid (H2CO3) which then slowly breaks down into CO2 and water. Since the excess hydrogen ions are used in the reaction, the pH does not change very much. Over time, as the carbonate ions are used up, the buffering capacity will drop and larger pH changes will be noted. From this it is clear why aquariums with low KH seem unstable - as acid is produced by biological action, the KH is used up; when it is gone, the pH is free to drop rapidly as H+ ions are generated.



Last edited by Bob Wesolowski at 09-Sep-2005 10:38

__________
"To steal ideas from one person is plagiarism; to steal from many is research."
researched from Steven Wright

Thanks for the info on Hardness, yes the 7 dH is General Hardness. You mention that GH doesn't really affect pH unless it's very hard (which 7 isn't) and that pH dropping is an end result of the nitrogen cycle, but it had only been 3 weeks (max) since my last water change. Can pH really drop that much that quickly or is something else going on?
Thanks!

Last edited by skeletaljosh at 09-Sep-2005 16:03

Mmmm, let me think... YES!

Three weeks since your LAST water change? If your tank has been set-up for a few months, three weeks is OK once in a while but most people like a minimum of 10% to 20% water changes each
WEEK!

Let's assume that your fish put 1 part of something into your tank every day. At the end of 21 days, you have 21 somethings in your tank. If you did 20% water changes every week, you would have just 14 somethings in that tank. Your water qulaity would be 1/3 better.

Of course, then you get people like me who do 30% every day... My tanks ranges between just 2.33 to 3.33 somethings in the water!

So, if you are doing 20% water changes every 21 days, your tank is going to stabilize at between 84 to 105 somethings in your water. If you start doing 20% water changes every day, you will drive the somethings down to 7 to 9 somethings in a week. The daily changes will markedly improve your water quality and allow you to stabilize the environment for the jardini.

Remember, pH changes are more detrimental to fish as pH declines than as pH increases!

__________
"To steal ideas from one person is plagiarism; to steal from many is research."
researched from Steven Wright

jardini??
Are you confusing me with someone else? I wasn't aware I had any jardini...
Thanks for your input and I'll be sure to keep it in mind.



Last edited by skeletaljosh at 10-Sep-2005 13:36