I would leave the gap unsealed so you can pull tiles to clean --- many have grouted etc and regretted doing it because they then can not pull them to clean -- I use a thick shop paper towel under my tiles to catch the urate that runs down in between - I pull the tile clean it w/ vinegar/ water 50 50 in a spray bottle and replace the paper towel that is wet --- here is a pic of one of dragons tank
Karrie