I would watch your pH, etc. for a couple days just to make sure no changes with the lid. I'm also not sure that unless you put a top on that basically seals the top, that the water will not evaporate. However, there was a recent thread about lids - not showing much difference in the parameters. I would strongly suggest if you are planning fish, that if you need to go away - that someone check the tank daily. Just from my disaster experiences when I went on vacation....I'm sure an ATO will not be able to TO for such a long time, I basically close tanks so that the evaporated water goes back to the tank