What about RO water for a FO tank?

no RO water isnt needed. Jus properly mix and age your water then cycle ur tank. U can either do it with fish or fishless. Definately get some LR! and as for substrate I recommend crushed coral. Plus your going to need some ph,nitrite nitrate test kits

What fish are you interested in having?

Contact your water utility and ask for the latest water chemistry report. This will give you some idea what you're dealing with, and help determine if tapwater will work. If it's high in nitrates or phosphates, you'll want to consider alternatives. Ditto for heavy metals.


For substrate--a lot will depend on what fish you want. I prefer sand--it's easier to keep clean, and doesn't trap solid wastes like crushed coral will, creating what's known as a nitrate trap. All those solid wastes break down and make it difficult to keep nitrates low. The fish you want will also play a role.

Live rock is the best biological filtration you can buy--much better than the power filter. Will you be adding crabs, snails, stars, etc? You can start out with 15-20 pounds of live rock and the rest (about 50-90 pounds) of lace rock. The bacteria will colonize both, providing all the biological filtration you'll need. Add in some critters, and you've got good mechanical filtration. The rock also gives the fish cover--very important for their long term health.

Fishless cycling would be preferable--less stress on the fish, less stress on you, and no concerns for removing the hardy fish used in the process (or dealing with their aggression later on!).

Blennies, gobies and clowns will all be safe with a variety of inverts, but hawkfish are hit or miss. They tend to go after shrimp. But--the inverts are the best mechanical cleaners available. Much better, and lower maintenance, than a power filter that can't get into nooks and crannies.

In SW, the sand is cleaned up by the snails, crabs, stars, etc. I've never seen solid waste build up on my SW tanks with sand, where in my FW systems, I have to clean the sand with a siphon over the surface. This just isn't needed in a SW system. With CC, you do have to clean it, which is complicated by the beneficial animals that live in there--you end up killing them or removing them. Plus, CC will trap solid wastes, no matter how frequently you clean, and this will contribute to higher nitrate levels. Fish typically are okay with lightly elevated nitrates but many inverts are not.

Silica works just fine. It's what I have in my nano, and there have been no problems with algae issues, or even pH stability. 3-4 inches is a good range for the sand. For the initial fill, you can mix the salt into the water in the tank. For water changes, it's important to pre-mix the water before adding it to the tank.

The DI unit does something totally different than carbon. If the additional carbon is before the RO membrane, it will help some to extand the membranes like, but carbon has to be replaced frequently to remain viable, especially if there are a lot of chemicals it will be removing from your water.