I have a 5.5 gallon tank with about 5 adult shrimp,10 baby shrimp, planted, sponge filter,driftwood, and some rocks. Every time I do a 50% water change I get high nitrates in a day or two. Nitrate goes up to 40ppm which is very bad for my shrimp. Does anyone have any advice as to why the nitrate is so high? I usually feed the shrimp every other day with 4 pellets of Hikari crustacean food. My tap water has about 3-5ppm of nitrate. I also drip the water back in to my tank during water changes as to not shock the shrimp.