Water tests

To keep an eye on the quality of the water in my aquarium I regularly do some water test for a number of water values. On this page I will describe which tests I use in my aquarium en wherefore I use them followed by a description of the brands of the tests. At the bottom of this page I will also show a number of test results from my own aquarium.

The tests I use

I use a number of water test in my aquarium to check the quality of the water in my aquarium. Below I will describe these tests, divided in three categories. The three categories are test for the benefit of the fishes, test for the benefit of the plants and test to prevent algae growth.

Tests for the benefit of the fishes
The check if the water values in my aquarium are right for my fishes I use three different tests. These test are tests to measure the acidity (pH), the sum of earth alkalines (GH) and the nitrite level (NO2). The right acidity and GH are just as important for the health of many fishes as the temperature of the water. Through the pH and the GH test I can check if the water values of my aquarium are right for the fishes I have in it. Especially the pH in an aquarium can change easily through a large number of processes and is therefore a value that must be checked regularly.

The nitrite test is especially important for a newly set up aquarium. Especially in a newly set up aquarium there can be high nitrite levels which can be lethal for the fishes in the aquarium. With a newly set up aquarium it's very important to test the nitrite level to prevent fishes from dying. When an aquarium is running for a longer time this test isn't very important anymore because nitrite problems seldom happen when an aquarium is running well.

Tests for the benefit of the plants
I personally are a fan of an aquarium with a large number of plants in it. To get optimal conditions for my plants I use a CO2 system and plant fertilization, but these products also bring risks with them for the fishes and can possibly lead to rapid algae growth. To minimize these risks I use a number of water test. To check my CO2 system I use a pH (acidity) test and a KH (carbonate hardness) test. With the results of these test and the table below I can check the CO2 level in my aquarium. For this purpose I also used a CO2 test from the brand Tetra for a while, but this test was inaccurate and therefore I now use the method with the table below.

Tabel: optimal CO2 level

    To many  CO2 Optimal  To less CO2
Increase hardness of the water KH\pH 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
0.5 15 9.3 5.9 3.7 2.4 1.5 0.93 0.59 0.37 0.24 0.15
1.0 30 18.6 11.8 7.4 4.7 3.0 1.86 1.18 0.74 0.47 0.30
1.5 44 28 17.6 11.1 7.0 4.4 2.8 1.76 1.11 0.70 0.44
2.0 59 37 24 14.8 9.4 5.9 3.7 2.4 1.48 0.94 0.59
2.5 73 46 30 18.5 11.8 7.3 4.6 3.0 1.85 1.18 0.73
3.0 87 56 35 22 14 8.7 5.6 3.5 2.2 1.4 0.87
3.5 103 65 41 26 16.4 10.3 6.5 4.1 2.6 1.64 1.03
Optimal hardness 4.0 118 75 47 30 18.7 11.8 7.5 4.7 3.0 1.87 1.18
5.0 147 93 59 37 23 14.7 9.3 5.9 3.7 2.3 1.47
6.0 177 112 71 45 28 17.7 11.2 7.1 4.5 2.8 1.77
8.0 240 149 94 59 37 24 14.9 9.4 5.9 3.7 2.4
Decrease hardness oft the water 10 300 186 118 74 47 30 18.6 11.8 7.4 4.7 3.0
15 440 280 176 111 70 44 28 17.6 11.1 7.0 4.4
20 590 370 240 148 94 59 37 24 14.8 9.4 5.9
CO2-level in mg/l, carbonate hardness in ºdKH

To use the right amount of fertilizer for my plants I use an iron (Fe) test. Because one of the main ingredients of aquarium plants fertilizer is iron, an iron test can be used to check if you use the right amount of plants fertilizer. This because the advised quantity of plants fertilizer by manufactures is in my opinion much to high and also I don't think that every aquarium has the same needs for fertilization. Therefore if you use fertilization for your plants you always need an iron test to check if you don't use to much. Otherwise you take the risk of getting an algae plague.

Tests to prevent algae growth
Algae growth in the aquarium is often caused by high levels of phosphate (PO4) and nitrate (NO3). Although the height of these water values aren't very important for the fishes the phosphate and nitrate level can be an indication of possible problems with algae. I personally are curious about the relation between the phosphate and nitrate level in the aquarium and algae growth and therefore I do also use a nitrate test and phosphate test to check my aquarium water.

The brands I use

For the measuring the following water values I use the tests of the brand Dupla: degree of acidity (pH), carbonate hardness (KH), sum of earth alkalines (GH), nitrite level (NO2), the iron level (Fe) and the phosphate level (PO4). Only for the nitrate level (NO3) I use a test of another brand, namely of Tetra. For a while I used the nitrate test of but this test went bad pretty soon a couple of times and also one time is already wasn't good anymore when I bought it. Maybe this test was already to old, but this can't be checked because there is no fabrication data printed on the test. Therefore I switched to the nitrate test of Tetra, this test is less accurate but is also less expensive than the test of Dupla. With this nitrate test of the brand Tetra was also a nitrite test but this so inaccurate (gives a reading from 1 mg/l) that the fishes are almost dead before you measure some nitrite. Also it's wise to keep the test in a cold place so they don't go bad to soon. 

Water values of my aquarium

Below the last three measurements of my aquarium water are printed in a table.

















27-08-01 14:00 7 5-5.5 4-4.5 < 5 0 0.1 0.1 -
26-09-01 16:45 7 5 4 < 5 0 0.1 0.1 -
03-11-01 14:30 7 5 4-4.5 5 0 0.1 0.2-0.3 -

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