Cycling tank with tap, then switching to RO/DI unit?

[thomascummins]

Okay, so I'm pretty new to the hobby, though I did have some experience with it back in marine biology class in high school (we literally just maintained saltwater tanks the whole semester). I am starting a 29-gallon fish-only tank that will ideally consist of a pair of clownfish, maybe one other small fish, and some inverts.

So I've always been hesitant about buying an RO/DI unit, only because I don't know where in the world to store the water while I live in a tiny college apartment. We also only have a kitchen sink and one shower between the three of us, and I don't know how long it would take to have that water get through the system. Other than that, I would absolutely pay to get the RO/DI system.

Whether it was a rational decision or not, I decided to begin cycling the tank a couple of days ago with TAP water (dechlorinated, with the salt added in of course). Assuming that I can find solutions to the problem above (and I'll take any suggestions you might have), I will order an RO/DI unit. However, here's my main question: will it be alright to at least cycle the tank with the tap water, and then start changing out the water until it's primarily water from the RO/DI unit? Or should I totally discard what's in the tank, wait for the RO/DI unit, and start over?

The one thing I want to avoid is getting a lot of hair algae all over the new LifeRock that's in there. I know it won't grow on it immediately, but I don't know if starting with tap and then transitioning to RO/DI would prevent that algae from growing, or if starting over is the only way to be sure. However, if you all think that the transition from tap to RO/DI would work fine, I'd rather go with that, just so that I know the money I spent on the salt wasn't a total waste.

Thanks for your help!

 

[Woodyman]

Doing a fish only non coral tank you may even be able to get by without RO/DI depending on the quality of your source water.

At the same time though I would use RO/DI. If you already filled with tap there isn't any reason you can't cycle with what you've already got. After the cycle and prior to any livestock just perform as close to a 100% water change as you can. Your bacteria will live in through the filter/live rock and all surfaces. If you really want you could also perform 2x of the 100% changes, but I think one would be sufficient.

You did mention a college dorm, I don't know where you go to school but most science departments will have an RO/DI system for producing lab quality water for research purposes. If your at a smaller school maybe not but it may be an option where you could get high quality RO/DI for free.

 

[Saltyreef]

Tap water is fine for fish only tank.
Keep an eye on your nitrates.

 

[Joe31415]

Off the top of my head, and I may very well be wrong here, tap water can (does?) contain silicates and phosphates, both of which can create their own problems.
As for the RODI unit. You don't have to store all that much water. The water for initially filling the tank goes in the tank, so that's an easy one. The water for water changes can be handled with a 5 gallon bucket. Fill a bucket up with RODI, add your salt, put power head in it overnight and put a heater in it a few hours before you do the water change.
The only real long term storage you'd need is for topping off. But even that can be done on a day to day basis. Make a mark either on the tank or if you have a sump, in the return section, where you want the water level to be. Take a look at it once a day or so and if it's low, make some RODI and toss it in.

For a small tank and limited space, I think you could get by with a few 5 gallon buckets (stacked when not in use). You're going to need to do water changes anyway, so you'll for sure need them. You could use one of them to store RODI between water changes for topping off.

 

[Woodyman]

I wo

Off the top of my head, and I may very well be wrong here, tap water can (does?) contain silicates and phosphates, both of which can create their own problems.
As for the RODI unit. You don't have to store all that much water. The water for initially filling the tank goes in the tank, so that's an easy one. The water for water changes can be handled with a 5 gallon bucket. Fill a bucket up with RODI, add your salt, put power head in it overnight and put a heater in it a few hours before you do the water change.
The only real long term storage you'd need is for topping off. But even that can be done on a day to day basis. Make a mark either on the tank or if you have a sump, in the return section, where you want the water level to be. Take a look at it once a day or so and if it's low, make some RODI and toss it in.

For a small tank and limited space, I think you could get by with a few 5 gallon buckets (stacked when not in use). You're going to need to do water changes anyway, so you'll for sure need them. You could use one of them to store RODI between water changes for topping off.

You are correct.

Tap water can contain any number of harmful substances. Phosphate and silicates are just 2 of them. Nitrates, ammonia, aluminum, copper, lead, etc. Tap water can be loaded with any one or multiple of these based on your source water. Another reason I recommend checking with your science department and trying to save yourself the expense of purchasing an RO/DI but it's not a bad investment eventually I'm sure your taking the tank home and you will want it there.

That in itself is a good reason to go RO/DI regardless of moving when you start with pure water and mix in your salt it mixes up the same each time. Tap water will vary from place to place so at home and at at school you may have very different tap water your tank could flourish at school and when moving it home it could crash. From the different makeup of that source water. Starting with RO/DI eliminates that possibility.

 

[JumboShrimp]

What size tank? If it's small enough (20g?), and evaporation will be negligible enough, $3 a week in distilled water to top-off might be your only ongoing water expense (after initially filling the tank). Could be a hassle, though, if the grocery store is a long walk from your dorm.