I have three turtles so you can imagine how gross the water gets without some extra help. I initially had one bio-stone and within a week I could start seeing a considerable difference. Since the recommended amount is 40gal with a single, I got a second one. See the before and after with the two stones. This is within a two week period.

My fish tank is actually significantly cleaner and needs less maintenance. The Fish is healthier. The stone is hella rough for a betta so his fins don't approve, but he mostly gives the stone a berth. I put this rock right next to the bubbler so the good bacteria can move around. The water's been clear ever since I put it in. Even fewer algae build up.
When algae layer the top of the stone we clean the tank, but I basically don't have to clean the tank more than once a month, and it's just to get the poop out of the rocks and some algae off the bubbler tubing.
20 Gallon tank with a betta and 12 marimo, waterfall filter, 2 plants, 2 hides, and a bubbler.
The tap water in my city is INCORRIGIBLE and this rock plus lots of water treatment has saved my betta from a very stubborn bacterial infection caused by the tap water. I had tried 3 brands of treatment but none of it worked without the addition of the rock.

Wow I love this product! I bought this for my 20 gallon tank. It's been 4 days and I notice a huge improvement. I've only had a tank for a few months. Despite partial water changes weekly, my tank was cloudy and had a smell that drove me nuts. The tank is clearer after only 4 days and the smell is gone. :)

My second stone: I used the 1st one for 2 years. My water was PERMANENTLY clear. My fish, Charlie, has been thriving. Only when coming to write a review did I see the line about it only lasting about a year. So, I went and got another. While my stone was out, the water got cloudy very quickly. Within 2 days of the new stone, the water was and is crystal clear again.

My fish tank water was very cloudy, and despite several partial water changes, I was not able to clear it so I went searching for products that could help with this. I bought some ALGONE to help clear the water, and I also ended up getting the Bio rock. Someone at the pet store had recommended since he had one in his fish tank, so I bought a medium size rock for mine (I have a 36 gallon tank with a pretty good stock of fish).

Per instructions, once I received the rock, I soaked it for 24 hours in non-chlorinated water. (I dripped some dechlorinator in a tub of water and let the rock sit in that). At first, I had both ALGONE and the rock in there, just to really clear up the tank and after awhile, I removed the ALGONE and now I just have the rock and it is wonderful!
My tank is SO clear, I was never able make the water THIS clear myself, despite routine water changes and vacuuming. Fish is nice and happy!

The gentleman in the pet store said he had this rock for 2 years so far, and I think that's a great investment. I still clean and change water on a regular basis, but this rock helps keeping it nice and clear and cuts down on the amount of cleaning that is needed.

I'm definitely a believer in this rock :)