An important function of your septic tank is to hold wastewater for sufficient time to allow it to separate. Doing load after load does not allow your septic tank time to hold the water. If you're not on a dosed or timed system, you could be flooding your drainfield without sufficient recovery time. Try to spread water usage throughout the week and over a day. Don't forget to check the label of the detergent you select.
Phosphates are one of the nutrients that cause plants to grow, including algae in our waterways.