Besides water temperature and salinity, there are a number of water parameters that are important to maintain for the health of the specimens being kept. Just how important these parameters are, and what you have to do to maintain them will depend somewhat on the type of reef tank you are keeping. For our purposes, we can think of reef tanks as falling into ‘low demand’, ‘moderate demand’ and ‘high demand’ systems.

Most of the demands place on the system have to do with the skeletal growth of the critter being maintained. Soft corals only have small fragments of skeletons called spicules buried within their soft bodies. LPS and clams have heavy shells, which must grow along with the specimen, but this growth is generally relatively slow. SPS corals are pretty much all skeleton, and under the right conditions, very fast growing. They tend to extract large quantities of things from the water from which to build their skeletons. The chemicals that these corals use are mostly calcium as well as strontium, manganese and others. Other water chemistry items include iodine, vitamins, etc. These demands tend to be more constant from tank to tank and independent of what is being maintained in the tank.

The good news is that most of these chemicals can be measured using test kits. The bad news is that most of these chemicals can be measured using test kits. What I mean by that is some people can drive themselves to distraction measuring and trying to optimize the water parameters. For people with low demand tanks, this is not really very necessary as the tank will tend to reach a point of equilibrium if frequent small water changes are made. My small 20 gallon low to moderate demand system has been in operation for about 3 years and I have measured no water parameters (other than salinity and temp) for the last 6 months or so. It is useful and informative to take frequent (weekly?) measurements initially until the hobbyist understands the tanks dynamics.

On the other side of the coin are the high demand tanks. These tanks can and will rapidly alter water chemistry due to heavy usage by the inhabitants. It can be difficult to achieve a truly balanced supplementation routine in these systems, so frequent monitoring of the water chemistry and making adjustments to compensate can be very important. My 70 gallon tank was a high demand system which I found necessary to use additives daily and to measure water chemistry weekly to keep it carefully balanced.

Iodine and vitamin supplements

There are a great number of products on the market which promise to replenish iodine, vitamins and all kinds of misc. trace elements Which are depleted through protein skimming or biological activity.  There is little proof that these supplements are really required.  Iodine is generally accepted to be an important trace element to supplement, but my own results have been that it does not seem to make much difference.  The all in one trace replenishers are often vague as to what they actually have in them.  In most cases, heavy usage of these products can promote algae growth.  If you utilize these types of products, try to select one that at least has an analysis listed so you know what your putting in your tank.  There are many expensive products with wild, but vague claims on the market 'snake oil' that don't list their contents and there is much speculation that in at least some cases, they may do more harm than good.  If you use these products (and many reef hobbyists do), do not overdose and discontinue if you have any significant algae outbreaks.