I am a first time fish owner and kept my 20 gallon tank clean and fish alive for about 3 months. Then the algae started. I dosed with algae fix per instructions, vacuumed and tried several water changes. 50% of my fish died over 3 weeks and my water remained cloudy and green. When only 3 of my 18 fish remained, I surrendered them to the fish store, and decided to start over. I vacuumed out 20 gallons of forest green water. I added about 3 gallons, swished around the gravel and vacuumed again. I did this 6 times (18 gallons of water) before it was clear. I let the gravel and decor completely dry before refilling my tank. I washed my live plants thoroughly before adding back to the tank. I added water with conditioner and have had the filter going for 3 days. Once again there is algae growing on the gravel. Is the algae immortal or am I doing something wrong?