water

For last 6 years I run with success I think 125 mixed reef tank. Of course I use RODI water.Im thinking about setting Fish Only with live rock tank. My question is do I have to use RODI water or just Top Water with conditioner will be good enough? Those RODI resins are expensive and there is a lot of waste water too. But Ill do whatever is best for fishes. Please let me know what you guys think. I have also 2 more questions about different tank I will set up. Id like to set up Hospital < quarantine> tank for future livestock. I like 40 breeder but maybe I should set up 4' tank like 55 gal. Longer is better for fish. They might spent some time there so I want them feel comfortable there. And 3 question is what kind of filtration? HOB or Canister? In the future I might treat there with copper or other chemicals. Please let me know about those 3 questions. Thanks.

 

Basically your going to have to test your water source for the usual suspects, nitrates, phosphates, chloramines, metals...
Size really all depends on the fish types you will be housing in the tank. A 40 gallon breeder should be fine for most fish types. The larger the better, but a 40 g should do the job nicely.
Filtration for the QT or the display? For QT you do not want use charcoal during treatment or other media that may absorb or remove medication, this includes live rock. During treatment for actual disease or prophylatic treatment the tank is basically bare bones with an oxygen/flow source and hiding places ie: PVC....
If the tank is a long term QT you can get more elaborate.

 

Thank you for reading my long post. and answers.If it comes to first question. But using RODI water is not a must, right? Fishes are not sensitive as corals. If tap water in the area is good quality I can get away with just conditioner, right? The third question. Yes it might be more long therm. What filter would you suggest then? Thank you.

 

You're right RO/DI is not a must for fish only tanks. Elevated phosphates and nitrates will lead to troublesome algae growth down the road. Chlorine is easily removed or allowed to gas off when the water source is left to stand for a day or two. Chloramine is a bit more complicated ( you'll need to research that topic).
Just to rule it out I would test for copper at least once just in case you want to keep some type of clean up crew or simple corals in the future. The LFS should be able to preform that test if you're a routine customer.
I know hobbyist that use canisters on their QT systems and adapt the medium as indicated by the use of medication. A canister with floss or sponge can help to support the biological filter. A simple HOB filtration can do the same but to a lesser degree, some take advantage of a skimmer. The more complicated you make the QT the more complicated treating the tank should disease show up or you routinely treat prophylactically for disease.
When all is said and done you need a biological filter. When using medication that discourages or destroy those bacteria you need to do water changes to prevent ammonia spikes.
Over time you'll modify your QT to meet your systems specific needs. Avoid over stocking a newly set up tank, monitor for ammonia and nitrites and intervene as indicated (prime or similar products are band aids). Having additional mixed saltwater for unexpected water changes will be an advantage until the QT becomes routine and you know the tanks personality.

 

If its worth doing, its worth doing right from the beginning.
Fish are a higher life form than corals or rocks so why not provide them the best? Why cut corners to save a buck or two when you may end up replacing fish later at a much higher cost? Its not worth the risk when you alone can have 100% control over your water quality AND water stability which you will not get using tap water.