Few words on PH

Few words on PH

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pH refers to water being either an acid, base, or neither (neutral). A pH of 7 is considered "neutral", a pH below 7 is considered "acidic'' and a pH above 7 is Considered "alkaline''. A pH of 5.5 is 10 times less acidic than water at a pH of 4.5. a rapid change of as little as .4 in either direction can be deadly to fish!!

Acidic = Low PH
Alkaline = High PH

If there is a problem with the buffering capacity(the ability of a solution to resist changes in pH.) of your water You  most likely have very soft water which means it is susceptible to wild swings towards the acidic PH range (Low PH).

If you look up key words like:
buffering capacity
PH
water hardness
Water softness
in Google you will find tons of information explaining the concepts in full detail.

"The Relationship Between pH and kH"

"kH is a measurement of the carbonate hardness of your water. In other words, it measures the concentration of carbonate and bicarbonate ions in your aquarium. kH also indicates your water’s buffering capacity – your water’s ability to neutralize added acids without significantly changing the pH. Therefore, a higher kH corresponds to a more stable pH in your aquarium and a lower kH can correspond to large swings in the pH. Generally, if your kH is below 4.5 odH, you need to closely monitor your pH for large changes. You will also need to be more consistent in your water changes as the low kH will cause the pH in your aquarium to consistently drop with time. Frequent water changes are the best way to keep the pH up to an appropriate level."

You basically have 2 options to resolve a low PH with low buffering capacity situation:
1) Additives

adding calcium carbonate (CaCO3). 1/2 teaspoon per 26 gallons of water will increase both the KH and GH by about 1-2 dH. Or simply add some crushed sea shells, crushed coral, limestone, marble chips, etc. to your filter.

adding sodium bicarbonate (NaHCO3), (AKA: baking soda). 1/2 teaspoon per 26 Gallons raises the KH by about 1 dH. Sodium bicarbonate drives the pH towards 8.2.

2) Do very frequent water changes

*Note* All quantities listed are approximations because it is not possible without having many other variables to be precise in the amounts needed to effect specific changes. The best thing you can do is get the proper test kits and use the above techniques and slowly adjust then test then adjust some more.

  R/O is of no help in low PH/Buffering capacity situations, because it has no buffering capacity thus would basically leave you in the same position you are in now.

*Note* Once you do go down the road of altering your PH please note you are forever chained to keeping a close eye on it and making sure to adjust as needed.

**Note** In a situation of a tank with low buffering capacity even the nitrification cycle (Which releases Nitric Acid as a by product) would change the PH over time. .

ANY rapid change in PH above or below .3 can kill fish and often will depending on the species and its resiliency to such activity.

Without testing we do not know what his KH and GH values are. They are not the same thing GH will not directly affect pH although "hard" water is generally alkaline due to some interaction of GH and KH. Thus often they should typically be discussed in the same subjects. You may have personally observed stronger reactions to changes in GH because different species of fish prefer different KH and GH values and changes in GH can effect KH which in turn effects PH if there are already elements in the environment trying to shift the PH but being held in check by the KH.
For those who might be rusty on this GH is simply the General Hardness of water (measurement of Magnesium and Calcium ions in the water). This is the reading that people are generally referring to when they speak of "Hard" or "Soft" water.
General Hardness Table
0 to 4 dH 0 to 70 ppm Very Soft
4 to 8 dH 70 to 140 ppm Soft
8 to 12 dH 140 to 210 ppm Medium Hard
12 to 18 dH 210 to 320 ppm Fairly Hard
18 to 30 dH 320 to 530 ppm Hard

KH (Carbonate Hardness) often referred to simply as Buffering Capacity = on the other hand is specifically and simply a measurement of the alkalinity. Which is a measurement of the waters buffering ability, or its ability to absorb and neutralize acid.

So anyway if we look up our fishes needs you will often see most fish prefer GH in the mid range of the scale. So since they do effect each other although indirectly it is best if you find you have a buffering problem to check for soft or hard water as it will also effect the longevity of your fish.

All of this leeds me back to one of my most common suggestions which is if you test your water and see what it is and buy fish that fit the water you have you have far less things to worry about. Otherwise know what you are getting into. and Knowing what you are getting into is half the battle...:)