What we all should really be measuring
This log was inspired by a disappointing article about reef aquarium lighting in the 1/2009 issue of Coral magazine written by Mr. Calfo. It repeated the same old mess of watts and water volume that has left hobbyists in the dark (pun intended) since the beginning of our hobby. There are so many variables affecting the actual light field inside aquarium that you just can not say that a species X does best under a 250W HQI, for example.
Why is it that huge majority of hobbyists never measure Photosynthetically Active Radiation, PAR (measured as photosynthetic photon flux, PPF) falling on to their corals? This is one of the most important parameter affecting the health of captive corals and other sessile invertebrates and yet 99% of hobbyists have no idea about PAR levels in their aquariums. There are a lot of scientific data about different PAR levels where certain coral species are found and it is one of two parameters that actually change radically in nature (the other being water flow, or water velocity).
If more people where measuring PAR levels in their aquariums the communication about placing corals would finally become possible. Now hobbyists use terms like “middle of the tank”, “low light” and “intensive” when describing the light field. These terms mean absolutely nothing to absolutely no one! What’s more, human eye is not at all good in evaluating light intensity. For example, did you know that due to tunneling effect, you’ll find much higher PAR close to front window?
Imagine if someone actually told you that the fragment they gave you was maintained at 220 µmol·s-1·m-2 and thus you could place the new fragment in exactly same light level. No more guessing and coral bleaching. Also, discussing coral pigmentation and other husbandry issues on various web forums would finally make some sense.
PAR meters can be bought relatively cheap from Apogee Instruments, Inc. With the price of pH meter you’ll get a device capable measuring something that is much more important. In a properly maintained aquarium the pH will always be in acceptable range anyway.
The other very important parameter doesn’t even need any device to report. Water flow, or more correctly water velocity is, together with PAR, the most important environmental property for a sessile invertebrate living on the reef. Not that the chemical properties of the water are not important but they are always the same (or very close) for all coral reef species! So while you can measure calcium, alkalinity and phosphate to see if you can maintain even the most basic requirements for a reef aquarium, they are not very helpful in figuring out living conditions for a specific species. Light level and water flow are the two basic properties that can change radically in the coral reef environment.
As said, you don’t need any device to figure out water velocity. Just observe how much a particle in the water moves in a few seconds and report the value in cm/s. You’ll find a lot of invaluable data in scientific papers about proper water velocities for different species. For example, a velocity of 10 cm/s is a good staring point for most gorgonians.