I just saw that you were asking this. You probably need a heater to maintain the temperature, depending on how much the temperature fluctuates, you may think of investing in one. A 100W for that tank should be fine and not too expensive.
I think the filter is just fine for a 70L tank and should handle the tank. I would adjust it to the max flow as the fish you have needs max filtration.
The ammonia level is low, bit still toxic and deadly if it keeps going for a long time.
As you can see from you test, nitrAtes are increasing compared to tap water, so there is a cycle going.
You need to try to keep the ammonia by water changes as low to 0 as possible,even if it takes you a big daily water change. Eventually, the nitrItes should start rising, which is the second part of the cycle. Deal with nitrites the same way as with ammonia, water changes and keeping it as low to 0 as possible. Once that stage is over, ammonia and nitrites will be at 0 and the only parameter rising should be NitrAtes. This one is not toxic to fish, but still needs to be kept under 40ppm by weekly water changes.
Cleaning the gravel is good, but when the tank is still in the cycling process, you don't want to remove any good bacteria that helps, therefore I would try not to disturb it too much for the time being until you cycle your tank. If it is too dirty, then siphon the gravel at stages, but never siphon all of it at once. Start from one spot, then next water change another spot..
Don't worry about the Ph value. However, if you notice it starts increasing/decreasing,then there may be an underlying problem with the tank. The most important about Ph is to stay stable.
Keep testing everyday until you get those double 00s for ammonia/nitrites and good luck.
