EcoBio-Block Aquarium Water Clarifier (Small, 8–16 gal) | Volcanic Rock — Lasts Up to 2 Years — No Weekly Additives — Long-Term Water Balance — Safe for Fish, Shrimp, Frogs & Turtles

I've used this in both my larger cold-water tank (30 gallons) and in my 10- and 6-gallon tanks. These are great at maintaining water clarity, reducing ammonia, and helping keep the tank inhabitants happy. Yes, they are kind of ugly, so I hide them behind foliage in my planted tanks. And yes, you will still need to properly cycle and maintain your tank water quality. Overall, though, I find they do a really nice job of reducing the frequency of water changes and keeping the tank water crystal clear.These are particularly good at clearing up cloudy water in planted tanks with substrate, and I've used them extensively that way to strong effect.

After reading overwhelmingly positive reviews for this, I bought it. I was a little hesitant because it was rather expensive and I had trouble believing that it really would work that well. After it arrived in the mail I rinsed it out and left it in a chlorine-free water-filled tupperware for 48 hours (as per the instructions). Then I dropped it in the tank. Our fish tank had a serious water clouding problem that we couldn't seem to fix. We did bi-weekly water changes, tablets, water-based agents, and a bigger filter and nothing worked. After a day of being in the tank the water was noticeably clearer; we would see each other through the tank when we couldn't before. After about two days you could really see that the water was clearing up. It's been about a month now and the water is crystal clear. When we compared it to another tank in the house the water was completely different, with the non-bioblock tank being duller and somewhat cloudier. We only have to change the water once every two weeks now. It's FANTASTIC. I'll definitely be buying another one soon!

k so, i have a small betta tank, maybe just over 2.5 Gal. This rock was obviously too big so I took a hammer to it. Broke it apart to a few smaller pieces. And since this rock is too rough and I didn't want to injure my betta, I placed a few small pebble sized pieces in under the sponge of my filtration system. Seems to be working ok hahaha water levels are stable and crystal clear.... I'm not even sure if what I did made sense or correct but... It worked

Made my water slimy and gross!

I have a 20 gallon tank and keeping it clear has always been a challenge. After trying most other stuff, I went with this and was pleasantly surprised. Within a couple of days of putting this in the tank, the water cleared noticeably. In a few more days, it was perfect. The stone does need to be placed where you want it permanently, as it appears to fall apart in the water as the months go by. I tried to put mine near the air stone as recommended and it really does a great job. I don't think I'm going to get two years out of it as they said, but I do plan on buying another when this one is depleted.

Not only is the rock too big and unnatural looking but many pet stores have cautioned against them.

I have been using these stones in my aquariums for years. They keep my water quality perfect and clear. With very little maintenance I am able to keep my fish happy and breeding, my snails and shrimp thrive, and my water aquarium stays stable. I have had great success cycling a new tank in 2 weeks using this stone to! I won't have an aquarium without one of these stones now.

I was pretty skeptical this would work. Having had many small simple aquariums over the years these "miracle solutions" always seemed to fall pretty short of the mark. This is certainly the exception in my experience. I dropped this into a very new 2.5 gallon tank for my daughter 4 days after starting the tank with 3 guppies. The tank after 2.5 days was starting to get quite cloudy. Just about 24 hours after placing the stone in, the tank began to clear. Now at day 7 the tank is back to crystal clear water. I was shocked to say the least. Granted the tank was only 2.5 gallons, and only has a basic filter (with a super tiny charcoal filter) built into the hood, no air stones, so circulation is decent, but limited. I would certainly recommend this to anyone and will be trying them in any future tanks.