Tropical Fish Keeping - Aquarium fish care and resources

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mikedelo 09-01-2008 09:58 AM

Water test results - Questions
For the first time I decided to test for Carbonate (KH) and General Hardness (GH) in my salt water tank.

Is the General Hardness test only for FW? I ask, because the results explanation mentioned nothing about SW, just talked about FW.

The Carbonate test was to result in a blue color after the first drop. It displayed a pink color which turns red as I put more drops in. What do these results mean?

Also..... why should I test for Carbonate and General Hardness?


Pasfur 09-01-2008 11:19 AM

Due to the chemistry of seawater, only a certain amount of organic acids are able to be utilized by the buffer system prior to changes occuring in pH. Testing for carbonate hardness, more commonly referred to as alkalinity in the marine hobby, allows you to add buffers to your aquarium as necessary.

This is one of the most important weekly tests you will run in a marine aquarium. In addition to measuring alkalinity, you will need a calcium test kit. The impact of calcium on this buffering system is just as important.

You will want to measure the carbonate hardness (alkalinity) in DKH, because this is the most commonly used scale, at least on this forum. I keep my alkalinity between 12 and 14 DKH. Others keep theirs a bit lower, between 10 and 12 DKH. Anywhere in this range will likely be sufficient.

You also need to test calcium and add calcium to the aquarium as necessary. Calcium is generally kept between 400 and 450 ppm, with some suggesting up to 500 ppm.

Different aquarists have success at different levels, but the minimums of 10 DKH and 400 ppm are a nice starting spot for the new aquarist.

For the record, these same organic acids that deplete your carbon hardness are what interact biologically with the biofilter and eventually become Nitrate. This is yet another reason for everyone to utilize a strong protein skimmer, which removes these organic acids from your aquarium, reducing Nitrate buildup and reduces strain on your buffer system.

mikedelo 09-01-2008 09:36 PM

Thanks for the reply! Very informative!

My Calcium level is at 500, is anything more than this considered dangerous?

I will perform a test for both carbonate hardness and general hardness tomorrow after work, and post up the results.

Should I just forget about the general hardness test?

Just so you know what I am dealing with....

PH = 8.5 (Jumped up from 8.3 a week ago)
SALT = 1.022
IRON = 0
TEMP = 79 degrees

SKAustin 09-01-2008 11:49 PM

General hardness is a FW Measure.

As for the results of your test, It would be helpful if you could provide the brand name of the test kit you are using.

If I may add a bit to what Mark has provided on Alkalinity: Alkalinity, is a complicated topic. For the purposes of the aquarist, it is primarily the measure of the bicarbonate and carbonate ions in the water. There are several other ions in the measure of Total Alkalinity, but these two make up about 96.5% of the total ions in the measure. Corals take up bicarbonate and convert it into carbonate with they use with calcium to form Calcium carbonate skeletons. Even some soft corals and sponges use these ions to form what are call spicules. Spicules are tiny skeletal fragments that allow for the animals some rigidity to their structure.

Here is an excellent, plain language article by Anthony Calfo outlining the Calcium/Alkalinity relationship and maintenance (take note of "The Marble Analogy")

The measure and maintenance of calcium and alkalinity levels in your aquarium are quite important, and as an added aside, special heed should also be paid to magnesium levels as it is also an important ion in seawater, which has a direct relationship with calcium.

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