I've come to realize my time and financial situation won't let me keep an awesome SPS tank. Mostly that an RO/DI system is going to be expensive and hard to set up in my apartment. I realize I can probably keep fish with tap. But what about stuff that comes from live rock? Is putting live rock into a tank with water made from tap going to kill off all the hitchhikers?

I imagine putting live rock into the tank and watching stuff flake off instantly.

Tap=algae

algae will be your biggest issue. But if you don;t have high lighting it won't really be able to grow. But even being next to an open window might be enough. So make sure that you have it in a fairly dark place with only minimal lighting and you'll be fine. But if you want to keep coral at all the lighting required to grow it will make the algae go crazy.

You might also consider buying pre mixed reef salt at your LFS that has been made with RO water. But this will be a pain for a large tank.

Why should fish deserve any lower water quality than corals?
Never use tap water for either. Tap water is inconsistent at best and you have absolutely zero control over its quality. Use only RO/DI and then you alone control your water quality.

Because generally they're less sensitive?

A long time ago I kept saltwater fish in water from the tap. Besides a discus tank, I've had a lot of freshwater fish live just fine in tap water.

If you're implying that I can't keep fish unless I use RO/DI water, then I'll take that advice and I won't. However, I thought things like water quality and lighting were scaled towards the demands of the organisms you had to keep.

Most hardy fish should do fine with tap but if you want enough light to see them then you are going to be constantly fighting algae.

You'll also be fighting the nitrates that are in the tap making your water changes less effective. A simple RO setup that you can connect to a faucet will only cost about $100 or less.

not necessarily. depending on the fish chosen for the FOWLR, the algae that (possibly) could be encouraged by tap water would be welcomed by snails, sea hares, urchins, etc.

I say possibly because we don't know the quality of the OP's tap water. it may be perfectly suitable for his needs, probably is. heck, it's probably perfectly suitable for the needs of a basic reef, given adequate herbivores and nutrient limitations.

You could also just buy RO or distilled water on a regular basis. I buy 6 gallons a week and it only costs about $1.50 and to be safe I use a TDS meter.

I kept a reef tank successfully with tap water in two different cities before we moved here. I discontinued using tap water here because I checked the water quality and found it is high in phosphates (and it contains high but not unsafe levels of cyanide). I would go to your local water dept and ask for a copy of their test results- these results are publically available to anyone.

additionally, they're also available online for most large water districts. for example:

http://www.lvvwd.com/assets/pdf/wq_summary_lvvwd.pdf

I would have little reservation about using my tap (Primed, of course) for top offs.

http://www.ci.baltimore.md.us/government/d...er%20Report.pdf

If anyone wants to take a look. It seems to be saying that my water will be coming in with 2 ppm nitrates. I feel like that's semi tolerable. I've yet to find anything that talks about phosphates.

http://www.advancedaquarist.com/issues/jan2004/chem.htm

Never rely on water quality reports from the Utility, they are a rough guideline only.
They are a snapshot in time and representative of only those sources and contaminants that were tested for in that particular round of sampling, I know, I'm a Water treatment plant supervisor by profession.

Tap water changes day to day or even hour to hour. A storm rolls in, treatment changes as do chemical additions and things like turbidity, pH, alkalinity, disinfectant residual etc.

Its not wise to spend dozens or even thousands of dollars on a fish or reef system and not have control of the water quality! Remember, wate ris the single largest ingredient in your system and everything in it relies on that water, why not provide the best you can. Its cheap insurance!

That's really funny, my husband was once a water-wastewater person as well (he's now an engineer). He's the one who told me the water was fine to use. A water utility tests their water every day, it's not just a "one-time snapshot".

They test certain things daily, usually only for process control and maybe chlorine and a few simple tests for compliance, thats it. They do not test things like phosphates and silicates daily. Many tests are only required every THREE YEARS, others once every four years, and some are quarterly or annually. They also have no control of what happens in the distribution system. What happens when the water main breaks down the street or Jor Contractor digs into it with a backhoe? Contamination. Does your utility add phosphates for corrosion control? Do they use free chlorine, chloramines or chlorine dioxide for a residual disinfectant? Do they do pH adjustment? Too many variables.

The water quality report is a way to please the EPA. It publishes test results which are from the previous calendar year and are of little value to a reefer. It only has to contain the test results from that calendar year, not things tested the year before or that were not tested in that compliance cycle. Never rely on it for anything more than a rough guide period.

Tap water changes according to sources and blends, in summer months they may run more wells to supplement surface water. In winter they may change the intake point to get away from colder water. On weekends and holidays they may again add more sources or change the belend to meet peaks. Nothing is consistent.

you make it sound like armageddon. while I generally wouldn't recommend tap water in a reef, I also wouldn't necessarily completely discount it. did you read through the advanced aquarist link I posted?

I've read that article many times. I prepared the annual report for the various utilities I operated for years and know everything they contain. I was around when the EPA encated the Consumer Confidence rule and was one of the commenting parties during its review and roll out. Been doing this for 35 years now!
The fact is tap water is inconsistent. We strive for consistency in our aquaria, we try to keep the pH, alkalinity, calcium etc stable. We use only good lighting and put it on a schedule. We buy only the best live rock, substrate and inhabitants. We need to do the same with our water since everthing else is secondary to the water. While I would not hesitate to drink tap water from any municipality in the US, I would not think about putting into my tanks. I have way too much invested to see it all go down the drain because I wanted to save $5 on some water. The cost of an RO/DI at $150 is very cheap in the grand scheme of things and it will save you money in the long run.

I'm going to get a straight response from my husband on this- because his take on it is interesting. He is more leery of RO/DI water than tap water. I'm not trying to say I'm right and you're wrong, it's just interesting to hear both sides of it.

Thanks for the input guys. I was really just thinking about getting my toes wet with a pair of Ocellaris and some coralline algae. I've got most of my equipment already, it's just that consistently running RO/DI is a big investment. Hopefully craigslist can turn up something.

I used tap for a year in my 5.5g but had to stop when I moved to a place with a lot more PO4.

I always tell people that tapwater is inconsistent but that they should feel free to use it if that's all they have. No offense to AZD, but If I would have listened to all the people who told me "You're doing it wrong", or "You can't/shouldn't do it that way" I would have been out of the hobby before I even started.

Do your research, then do what you have to do to get your hands wet. Who cares if your first system isn't ideal?

RO/DI is a very small investement really. I calculate my water cost at less than a nickle a gallon and that includes the capital cost of the unit, replacements, water and sewer costs and everything. Strictly water and sewer costs account for less than 0.5 cents per gallon.

My first MaxCap RO/DI paid for itself in the first year of operation and saved me from then on.

http://www.spectrapure.com/email/customer-...eciation.html#1

My first two reefs were tap water and it was 100% deep well or ground water at that time which was pretty good. The City switched to treated surface water and my reefs went to heck quickly. I bought my first RO system in 1990 and have never looked back. My son buys and sells saltwater tanks and uses treated tap water. He constantly fights algae and water conditions while I just keep going and going!