Well, you need to be on top of water changes first off. I wouldn't even be saying this if I didn't mean you had to be habitual. I was doing a 25% every week with fish but I'm cutting that to 10% a week now that I have no fish. Evaporation is absurd, I am in my apartment most of the time so I can manually top it off always but I have marks on the sides of the tank with the salinity readings the tank will read at various given water levels. Also, inverts and small fish dying happens all the time in larger tanks and we just never see them again, but in a tank this small you need to be on top of it right away to remove anything. I had 1 fish die in my tank, I removed it and did a 50% water change and set my skimmer up right away. It took my tank 3 days to stabilize to the point I was comfortable not taking readings every few hours. I've been lucky so far with deaths and spikes, they've only caused a minimal amount of loss, but it has been a learning experience for me.
Honestly, I took up a 5g knowing it would require more attention than something larger.