I agree with previous posts that a lid would definitely help reduce the water loss.
I've just had a similar problem to Daize with a tank I am currently cycling - day 4. Every morning there was water showing just under the front of the tank and I panicked thinking it had developed a leak - however it turns out that it was condensation running down the back of the tank which was a tad full and set on 29° so I've taken about 1½" water out and stuffed paper towel down the back to catch any excess moisture. No more water appearing at the front of the tank now - phew! Ammonia still at 4ppm but it's early days yet.