Ammonia test...

Greetings reefers! I just have a little confusion about the ammonia test lately. Ive been cycling my tank for about 3 weeks now. After 2 weeks of my cycle ive been getting different readings on my ammonia tests. Initially after the drops it will stay 0ppm for about 5-10 mins then the color will change after 15mins to .25ppm then couple more hours change to 0ppm again. Ive been testing my ammonia everyday and so far after 2 weeks ive been getting 0 ammonia nitrite 0 and 5ppm of nitrate. I did the raw shrimp method on my day 4 and after overnight my ammonia spiked 8ppm followed by nitrite spike and eventually getting 0 everything 0 after 2nd week. Ive been ghost feeding too with fish flakes after week to up to now. Any input will help. Thanks in advance guys