Wet gas cleaning equipment of AHLSTROM, that uses clarified water from sediment traps, was started at the Baltic Power Plant in Narva in 1993. It was induced from the feasibility to lower expenses of neutralizing sulphurous acid at SO2 catching by using clarified alkaline water, circulating in hydraulic ash removal system. Preparation of reactants (mainly of CaCO3 suspension) usually used for this purpose is very expensive. However, quite soon the exploitation experience showed that intensive growth of hard bound gypsum deposits on equipment surfaces became the main problem at its operation. Analyses showed that Ca2+ and SO42- content in these deposits were 60-80 % or even more indicating quite clearly their origin. The possibility to avoid gypsum deposits disturbing the operation of the wet gas cleaning equipment in the Baltic Power Plant by dilution of circulating wash solution has been studied in the paper.