2.1. Recirculating systems
Two water recirculating systems were used, with 12 (1 m3) circular
fiberglass experimental tanks each, located in a covered area. Tanks
were filled with 800 L of water, had a permanent water flow of
7 L min−1 and individual aeration with porous stones at the bottom
of the tanks. Underground water from a local well was used to fill the
systems with 16 m3 of water. In each system water was pumped to an
elevated tank from which it was distributed by gravity to the 12 experimental
tanks and then flowed through two concrete rectangular
sedimentary tanks. Subsequentlywaterwas pumped up again to the elevated
tank. The sedimentary tankswere cleaned and 40% of the system
water renewed every 3 weeks, beginning on the 6th experimental
week.