Blind level in the aquarium

There may be several reasons:

1-Decomposition - food or fish feces that is not sufficiently removed. filtration media
For any problem in the aquarium, the first priority is to change the water more frequently.

Insufficient filtration can also be a problem - it cannot remove organic waste that begins to accumulate in the aquarium (performance, insufficient amount of filter media for settling bacteria).

In aquariums without technology, fast-growing plants are used, such as

Ceratophyllum demersum - Rožkatec, Pistia stratiotes, etc.

These plants consume a lot of organic waste from the water for their growth, thus helping to keep the values ​​within the norm.

2-Fertilization - a substrate that contains nutrients, excessive addition of fertilizers, overstocking...

A substrate enriched with nutrients is not suitable for beginners, because it can do more harm than good. This will cause a lot of nutrients to enter the water and problems with algae, dead surface, turbidity, etc. Fertilization is not exactly a piece of cake, in order for the plants to receive all the necessary nutrients, it is necessary to have the right water quality values.
For example: PH affects the absorption of nutrients, high iron values ​​can cause a manganese deficiency, excess potassium causes a calcium deficiency, etc.
People like to use fertilizers even if their aquarium does not require it, sometimes you just need to give everything time.
Overfishing means a lot of biological waste!
Even strong filtration and a large number of plants may not save you from disaster.
Biological waste does not have time to be processed when overfishing, which results in turbidity, oily surface and rising NO3 and gradually NO2 values, which even with a small increase results in poisoning the aquarium inhabitants! Fish feces are fertilizer for plants, which also need to be kept in check.

3- Feeding - Some foods can cause a dead surface, but the worst is overfeeding!

The most effective way to get rid of the oily surface is to use a skimmer or aerate the aquarium!
There are also filter media - they help remove excess nutrients.
As a quick help are preparations (it is best to use preparations that help break down nutrients biologically)!

You always need to find the reason for problems:
Check if something is rotting in the aquarium, you need to have enough plants, a running filtration with enough bacteria, do not fertilize and do not have an overfished aquarium!

We wish you a lot of luck!