Etching tank
Hi asperri,
the etching tank you purchased contains an aquarium heater, which will get too hot and break if if the liquid level is under the heating element. Therefore this releatively high amount of etching solution is recommended.
The heater will become red hot heating the glass cylinder too. Causing movement of the etching solution by any means will break the cylinder at the point between "cool" and "hot".
Not using the heater the etching process takes a long time at room temperature. At 10degC it won't etch at all. (or just within a week or so).
The tank should be equipped with an air distribution frame at the bottom. This is very important for the mechanical work during etching. (The already etched copper has to be washed away by water movement to accelerate the process.)
The mixture should be 200g on 1l of water. Using 250g accelerates etching, but burries the risk of a crystallized etching solution at the tank buttum if the temperature of the solution rises above +55degC, which it does around the heater.
If cyrstallization occurs the only way to dissolve the concrete hard stuff is adding a little amount of water and lots of developer (natriumpersulfate). Do that
outdoors because those two chemicals react producing tremendeous heat and poisonous gases.
Hans