To say it straight at the beginning, we always recommend to exploit all possible options of biological regulation and control before using chemical agents. But anyone who is in the aquaristic hobby for some years has already experienced the situation, where all the tricks and tips from the biological toolbox are no longer helpful.
But before you give up with the aquarium hobby, you should consider all reasonable alternatives. But some basic aspects should be observed using chemical products. Whenever it comes to the use of chemicals in the main tank, you should if at all possible, test the compatibility with your own stock in advance "en miniature". For example, you can take the most sensitive plants or corals from the main basin and confront them in a small quarantine tank with the recommended dosage of the drug. Shows the plant or animal after a reasonable time (specified according to the effective time given by the manufacturer) no negative symptoms, one has at least a much higher level of security when used in the main pool.
With the given doses you should always be aware of how many liters of water (net) are really contained in the tank. A 100 liter tank are where 20 liters are used by decoration and where the actual water level is just a few inches less than the nominal-level, one can quickly end up with an almost 50% overdose. You should almost always use very conservative estimates, start low and increase the dosage slowly.
With the absorber products one aspect is particularly important. All agents work only if they are flushed from the water really effective. This means in most cases, that the simple mounting of a bag into the water, has no significant effect. Only the application in strong flow and if possibly in a special filter component enforces the permanent contact with the medium.