Alde fluid

Having done a flush and refill on my Alde in the 400, I can tell you that the reservoir tank would take a long time to completely evaporate. I would check for evidence for a leak in the Alde boiler area and also around the drain plug under the trailer (usually has a red plug pointing down). The reservoir itself is plastic and might have a crack that could leak. So a careful look around first followed by a cautious filling of the reservoir to see if any leaking is noted. Also I would think you could locate the tank cap unless someone removed it without your knowledge.