I have a maxi-jet 900 in my 20 gal tank. I was told there are dead spots ina tank with one powerhead. Should I get another one and if so what do you guys recomment I get? A smaller one or a bigger one or same size? And which manufactuarer is good? Also I'm on a tight budget, im currently a college student paying for school gas and car insurance so plz help me out. =)