Saltwater Aquarium Water Testing Answers

Q:  What should I test my water for?
A:  You should test your water regularly for ammonia, nitrite, nitrate, pH and carbonate alkalinity. If the tank is under two months old, these tests should be done at least every two days to keep track of the nitrogen cycle. If you have decided on a reef tank, you will want to test regularly for calcium levels. With a reef aquarium, you will want to check your alkalinity and calcium levels daily as a rule. These components are very important for coral growth.
Q:  What is the difference between milligrams per liter (mg/L) and parts per million (ppm)?
A:  The first, milligrams per liter, indicates the weight of a substance in a volume of solution (for example, 2 milligrams of iron in a liter of solution). Parts per million indicates the weight of a substance by weight of solution. For example, 2 parts per million could mean 2 pounds of iron in a million pounds of solution, or 2 milligrams of iron in a million milligrams (1 kilogram) of solution.

For all practical purposes the terms can be interchangeable in seawater, because the difference is small. The two terms are identical only when the liter of solution weighs exactly one kilogram.
Q:  What is the difference between nitrate ion and nitrate-nitrogen readings?
A:  Measurement of the various nitrogen compounds (ammonia, nitrite and nitrate) can cause some confusion regarding units of measure. What is being measured must be determined. For example, does a nitrate test measure the parts per million of the nitrate ion, one nitrogen and three oxygen atoms, or just the nitrogen alone. The latter, commonly used for scientific work, has an obvious advantage in monitoring the nitrification cycle in aquariums. The progression of the nitrogen in an aquarium where 1 ppm of ammonia-nitrogen is added ends up as either 1 ppm nitrate-nitrogen or 4.4 ppm nitrate ion. Both are the same concentration, but the first is easier to follow.
Q:  Which line is the correct fill line on the fasTesT® and Instant Ocean® test kits?

A:  The correct fill line is level with the top of the color chip once it is in place, as indicated in the drawing below.

Correct fill line on the fasTesT® and Instant Ocean® test kits

Q:  My reef tank has a lot of hair algae growing in it, and recently my aquarium shop tested the water and told me the problem was a high phosphate level. Could you tell me where the phosphate came from and what I can do about it?
A:  Your situation is common among miniature reef aquarists. There are several possible sources for the phosphate in your aquarium water: the salt mix, the tap water, the food and the activated carbon. Use your Instant Ocean® Phosphate test kit to verify the amount in your aquarium.

Phosphate is essential for algae growth. In situations where algae are desired, phosphate can be added to the water. Most salt mixes today do not include phosphate in their formulas, although some in the past did list phosphate as an ingredient. Phosphate has been found to be readily available from other sources, such as food and tap water. Phosphate is not added to Instant Ocean® or Reef Crystals® sea salts.

Food is a common source of phosphate. Whenever food is added to an aquarium, there will be some buildup of phosphate.

Certain kinds of activated carbon have been reported to release phosphate into the water. This ironically occurs with some of the highest grade products. Apparently, some “super-activated” carbon has been washed in phosphoric acid in addition to receiving the necessary steam treatment. The result is a product that has very high surface area but that also may have some residual phosphate. In any case, many of these super-activated carbons are not appropriate for water treatment. They are designed for air purification and quickly become clogged with the large organic waste molecules in an aquarium long before all of their micropores are saturated.

In a reef aquarium, it is better to avoid a problem than to cure one. However, there are some phosphate remedies on the market. Look for a reputable brand, which your local retailer should be able to help recommend. Water changes will also help lower phosphate, as will using filtered tap water (like reverse osmosis).