Can a small fish tank die without an oxygen pump?
No, just keep the right amount of water and feed it. Oxygen pumps are needed for larger fish tanks.
Yes, round cylinder is not good, change another.
If there is no oxygen pump filter would have less feed on time every day to suck out the fish feces, then add an equal amount of trapped and aspiration good water (need to be trapped for three days) for water, so only one point, can keep clean and oxygen injection water, more than a week (or see the water mix) a large water exchange, namely 3/1 for water. A few hours ahead of the storm well water on the water tank side before, so in order to guarantee to change the new water and the water in the fish tank to keep the same temperature, the fish will not be stimulated to.
