Ok, so why is pH so important for your fish and plants? Various aquatic chemical mechanisms change vastly
with differing pH’s and the toxicity of certain metals and compounds changes with pH, what does this mean for
a balanced and safe aquarium? Not much, if you’re aquarium is balanced don’t stress, having a slightly acidic
or slightly basic pH isn’t the end of the world.
If your pH is between 6 and 8, I see no problems with keeping fish. There is normally no reason to adjust your
pH unless you are breeding specialist fish or are experienced. If your pH is a bit high, you can add peat to your
water, this will soften the water (coming up soon) and lower the pH by releasing Humic Acids. If your pH is too
low, add crushed coral, shell grit, dolomite, etc ( a quick google search will tell you what is and isn’t viable).
The most important thing about pH is to prevent wild pH swings, a mildly acidic or basic tank wont hurt your
fish, but pH that changes continuously will stress them, will wreak havoc on your tank chemistry and will be a
massive pain. Basically, when you are testing for pH you are testing to see if it is liveable for the fish, and you
are testing to see if it is changing with time. If it is changing, your tank is unbalanced and you have to do
something to rectify it, whether it be plant more plants, take out that big bubbling rock, again a quick google
search can tell you exactly what needs to be done.
As a general rule, don’t use pH Down, or pH Up to adjust your water whenever it is starting to shift, this is a
bad way to control pH and a good way to have wild and random swinging pH’s that will stress you and the fish
out, instead address the issue at the cause.
Naturally, in distilled water pH will swing quite rapidly for any number of reason, well, how do we prevent this?
The answer is buffers. Which is the next topic.
Buffers
Buffers rely on a chemical system called equilibrium. Equlibrium’s are reactions that will proceed both ways
based on the concentrations of the reactants and the products. An example of a common aquarium buffer is
the HCO3- system. Most buffers rely on a weak acid (or weak base) and a salt of the acid. Bicarbonate system
isn’t an exception. It relies on a few equilibrium equations:
CO2 + H2O <-> H2CO3
H2CO3 <-> H+ +HCO3HCO3- <-> H+ + CO3 2CaCO3 <-> Ca+ + CO3 2The basis of this is that when you change one of the parts of the equilibrium, the others adjust so as to
minimize the change. What this means in a very basic sense is that if you were to add acid to a solution
buffered with CaCO3 and H2CO3, the pH change would be less than if you were to add it to an unbuffered
solution. This allows the pH in aquariums to remain fairly stable despite the constantly changing H+ and OHgenerated in the aquariums. This is handy, because during the day, plants generate HCO3- ions, but at night,
they release CO2, this CaCO3 buffer prevents wildly swinging pH from day to night. This is the most basic
buffer system in most aquariums, there are softwater aquariums with negligible amounts of CaCO3 dissolved
in them, these utilize a different buffer system normally comprised of humic and other organic acids, I wont go
into that because it’s a big side topic. Diana Walstad has however, if anybody is keen to get her book (I have it,
it is excellent).
Before Moving on:
Please note, this is a thousand times more complex than I have explained, so don’t go adding straight
dolomite or lime or anything of the sort to prevent pH changes. You will do more harm than good. Crushed
shells, limestone, that kind of thing, is more acceptable, but research before doing so.
Well, you may be wondering, where does this Calcium Carbonate come from?
This brings us to the next topic
Hardness
There are two types of hardness, well, theres really not, let me try again, there are two measures of
hardness. Hardness is I guess a hypothetical thing. The water isn’t physically hard. Its still a liquid. God I’m