Thank you both.
For the filter pipe problem, I do have some extra filter sponge, so I'll try to fix that on the end of the pipe, thanks for suggestion.
I just ordered TDS meter online, it should be here in week or two. Didn't find GH test that can be shipped here yet, but I'll look again in few days (seller that is willing to ship is out of stock right now).
Distilled water is cheaper option (at least at the moment). I do have a water filter in my fridge, maybe that could be okay to use instead of the filter jug? Here is the link with specs of that fridge filter https://www.samsung.com/nz/home-appliance-accessories/refrigerators-filter-hafin2-hafin2-exp/
BTW, I just measured the tank I have. Dimensions are 35cm (l) x 18cm (w) x 24,5cm (h), water level would be at 22cm. So the volume is about 13,5l. Is that too small?