https://www.amazon.com/Bar-Keepers-Friend-Cleanser-Polish/dp/B00505GBSK/ref=sr_1_2_a_it?ie=UTF8&qid=1492699177&sr=8-2&keywords=bar+keepers+friend

This stuff worked really well on my aquarium. Combine with a good bottle brush. It uses a safe acid and is supposed to be eco friendly I believe. It is also fairly cheap.