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Sometimes it happens that in a mature aquarium water pH increase occurs despite the fact that aquarist acidified water that is used for water-changes. Elements of decoration or equipment placed in an aquarium may be responsible for it. The most common culprit may be a substrate or a substitute for the filter material placed in the aquarium filter. For example popular is to include in the filter LECA which porous structure is quite efficient substrate for the existence of beneficial nitrifying bacteria (aerobic) and, at the specific conditions, also for denitrifying bacteria (anaerobic). However, there are various LECA and sometimes it is not neutral for the parameters of water. The same applies to gravel or sand used as aquarium substrate. Also, certain items of equipment such as aerating stones may not be neutral for the water parameters.
If the aquarium water pH is increasing, despite the use of acidified water prepared in the correct way, you can try to do a test that can help determine the cause of increase in pH.
How to perform a test to see?
1. A very popular type of quick test is pouring a few drops of acidic substances (diluted acid) on inspected material/substrate. If the substance is to spume, it means that it will affect the water parameters. However, not every type of material can be 100% verify with this method, since in the case of materials that are very gently raise the pH of water, they may not effervescence in contact with acid, or we just do not notice it.
2. Another simple and reliable test to check the impact of the media, accessories or decorations on the parameters of water can be carried out as follows:
We should prepare two identical glass vessels (glasses, jars, etc.). In one of the vessels put the test item – a large pinch of gravel, decorative stone, etc. Then fill the two vessels with the same water. Leave the dish for 24-48 hours and after this time check the water parameters (pH and possibly hardness) in either vessel, using a reliable aquarium water test-sets or electronic pH- and possibly EC-meter. If the test substance (gravel or whatever) does not affect the water, the measurement result will be identical in both vessels. If the parameters of water in the vessel with gravel (or whatever) are different than in a container with water alone, this means that the gravel (or whatever) affects the parameters of the water and thus is not recommended for aquarium with discus fish.
I should also add that the initial parameters of water used in these tests do not matter because no matter what, after the specified time should be identical in both vessels, unless in one of the vessels, there is a substance which changes the parameters of water. It is important only that the two vessels were filled with the same water.