The reserve is shown separately for each direction, because hryvnia on a card and USDT on the TRON network are different pools, and a large balance in one says nothing about the other.
What to do if your amount exceeds the reserve
Split the exchange into parts or agree the amount in advance. Large exchanges are usually doable, but they need preparation rather than instant settlement.
Why the number changes during the day
Every completed exchange lowers it, every top-up raises it. A reserve that has not moved for days is worth a closer look: either it is not live, or the direction is not working.
What the reserve actually tells you
It reflects working volume, not the wealth of the service. An exchange does not keep all its funds in one place: part sits on exchanges, part is in circulation. The number shown is what can settle a payment right now.
So a huge reserve is not a sign of reliability, and a zero one is not a sign of trouble. What matters is how it compares with your amount, and nothing else.
How to read the reserve before an exchange
Compare it with your order. If your amount takes up a noticeable share of the reserve, it is sensible to agree the exchange in advance: that way the rate and the timing are known before the money is sent, not after.
If the reserve is smaller than your amount, the direction can still be completed, but not in one step and not instantly.
Read more: Why the top line of a monitoring site does not mean «the best»