If you have time, you'd better go every day. You don't have to swim a long distance, mainly because the intensity is higher. You can swim 50 meters in groups of three, and try your best every 50 meters. After swimming, take a pulse 10 second. If it is more than 25 times, you should try your best, and then rest until the pulse of 10 seconds jumps to 18, and start the next 50 meters. After swimming a group, you can rest until your physical strength is fully restored, so it is enough for a group to swim about 3 groups. I once lost six pounds after swimming like this for a week.