I don't get much evaporation though. The volume is 130l. Should I take out some and replace it, and what should the replacement water be (1.026) ?
You could do 3 water changes, one every 2 days, replacing about 33% of the water with 1.027 water. That would get you to 1.025 in 6 days (3 water changes, 130L new water)