How much of period flow is actual blood and not other fluid or tissue? have read "normal" blood loss only 2-4 tbsp, but that doesn't seem like much.

See below: About half of the fluid in menstrual flow is blood. In terms of actual blood loss as normal (<60 mL blood), moderately heavy (60-100 mL), or excessive (>100 mL). Iron deficiency anemia is common in menstruating women and you may wish to take oral iron and multivitamin supplements, especially if your blood loss is more than normal. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex.