Generally, three side of reef tank glass might be cleaned, if it is really need for that. This may be when the glass is turning green or brown or sometimes there are purple round spots. All this means different meaning. Green happens when there is too much food or lights are on too long – so, please, do not over feed or play around with light timers! Brown color on sand or glass means that something died and backteria is growing in the tank. Water change is needed! Violet round spots are normal, so no worries!
Glass cleaning in this tank might be difficult because tank is small and has hanging rocks and corals and macros are close to glass. But it can be done, as I did it before many times. There many ways of doing this. For you try first unplug two white and black cable on the bottom stand like during feeding. Use magnets to clean the glass in the areas when magnets does not touch anything else. Go slowly, very slowly. Back and forth few times. At some point, you have open the lid like during feeding , so remember all steps and do not break the top glass!
After properly open lid, using skinny brown long stick, move things around and use magnet to clean glass. You may need to remove water pumps on the left and right sides one at a time. Start with left one – lift it and place onto blue sponges. Slowly remove green sponges, so dirt will not fell into water and put it inside the plastic round container that is below tank. Clean the glass all around till you come close to hanging rock – now, move the rock close to middle of tank so magnet does not touch it... and slowly go around towards the right water pump.
Now go to next chapter of cleaning water pump filters.