Can clutch fluid be low for any reason other than a leak?

I’ve had two top up my clutch fluid two times in a few days though it hasn’t gone low today.

I was looking for the leak which I believe can only occur in clutch fluid container, master cylinder, slave cylinder and related pipes however I cannot are leaks anywhere. I previously thought there was some fluid under the driver footwell however this may have been caused by a significant rain boot leak from rear when I was on a slope, maybe not. In any case I can’t really see any leak from aforementioned parts. Engine bay is quite dirty.

Could it be that there is no leak and maybe the two rounds of fluid I added got drawn into the system and will not leak further?

Or does the description suggest their is definitely a leak somewhere so no point in thinking about bleeding contaminated fluid etc until I find that?

Also from the pic you can see there is black stuff in the clutch fluid container. After adding fluid I can already see particles in it(not noticeable in pic). Gears have started to become hard again despite adding fluid.

Also if the clutch fluid is slightly more than max would that cause any problems?

Thanks.