Planted aquarium enthusiasts have long known that
carbon dioxide (CO2) is the limiting nutrient in their tanks, and that tanks with
CO2 supplementation can have aquatic plant growth that borders on the miraculous.
But adding CO2 means tracking its concentration — too low an addition rate or excessive
water movement can result in insufficient CO2 levels, whereas too much CO2 can stress
or even kill fish. A pH measurement and control system is the best way
to know and control CO2 and pH levels, but for many people the equipment required
has been prohibitively expensive.
The answer to this dilemma is to build your
own pH measurement and control system, something which is within the budget and
skill of many aquarists. This pH measurement and control system has been made
as simple and straightforward as possible. The idea was to make it an fun
and easy project, even for people without a lot of of electronics experience (but
see the disclaimer at the end of this article).
It was was designed to be reliable and forgiving. For example, electrical
"noise" from the aquarium lights and heaters (a common problem) is filtered
out in this circuit so that even an input with a lot of AC noise will give good
results. Finally (and importantly for many) this circuit was designed using
inexpensive and easy-to-find parts — everything for this project is available from
the local Radio Shack store. (The one exception is the pH probe, which is available for about $40 from Amazon.com.)
The less electronically skilled, the less ambitious,
and the busy may want to consider building
the simplest possible pH meter or just
buying a pH meter.
You can print a copy of this project's complete schematic diagram if you want to have it available
as you read the explanatory text.
There is a parts
list as well. Note that there aren't many parts: an inexpensive
ph probe, two op amp ICs, a voltage regulator IC, a power supply, some sort of display
(a voltmeter or panel display), and some passive components (resistors and capacitors).