We have an Aquaclear 70 HOB filter for our 29G tank. How often should I clean the sponge and bio media? I believe I am supposed to swish them in some tank water in a bucket? We just started the tank a few weeks ago and had 6 fish and unfortunately have lost 2 already?? The LSF tested our water and see no issues. The readings are 0 ammonia, 0 nitrites, 5 nitrates and the PH is 8.0. We do not have live plants. We have some silk plants and I have noticed some brown stains starting on some of them. Water is clear and no signs of algae. Any thoughts?