Store purchased RO water

[Rob in Puyallup]

I've used distilled water for my 10 gallon reef tank since I first set it up about six months ago. All seems to run perfectly using this instead of RO water. I do weekly 1.5 gallon water changes...

I just found out that the local grocery store sells RO water through a dispenser, a fill your own jug kind of thing.

Are there any tests used to check RO water, to make sure that it is? I have the standard kits as well as a TDS meter.

Thanks!

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[Wankell]

TDS is all you need to check, just make sure the TDS is as close to 0 as possible. If you didn't know, TDS stands for Total Dissolved Solids so it will pick up something if anything is in the water.

 

[Ron Reefman]

TDS is all you need to check, just make sure the TDS is as close to 0 as possible. If you didn't know, TDS stands for Total Dissolved Solids so it will pick up something if anything is in the water.

+1
Just remember, you can have a TDS reading that's high (like 30 TDS) and if it's due to calcium chloride (or some other non-harmful substance) in the water and it's not an issue at all. On the other hand, you could have a very low reading (like 2 TDS) and it's due to copper or lead (both used in older plumbing) and it will kill everything in your tank. We want zero TDS just to be safe. But I have a friend whose house water is 100-120 TDS and he didn't use an RO/DI system. He used that 100 TDS water for years and had no issues in a very mixed reef with some sps corals.

 

[Rob in Puyallup]

So I should be convinced the water is good if it's zero TDS. I'm guessing pH would be neutral as well.

Would nitrates and the rest show up as dissolved solids?

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[Rob in Puyallup]

Curious if RO water is that much better than distilled?

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[AZDesertRat]

No RO is not better than distilled. RO/DI should be your first choice, distilled second choice and RO only third as it will contain TDS since RO only is only a 90-98% efficient device.

I do not trust vending machines, you are at the mercy of the vendor as far as maintanance or lack thereof. RO vending machines are intended for drinking water so TDS is not an issue to them, its the TDS that makes water taste good. Machines are not regulated by health agencies, usually only by the dept of weights and measures to make sure you get 1 gallon for your quarter or whatever.

If you must buy RO only water, find a staffed water and ice type store where they are usually very proud of their product and will test the TDS or conductivity in your presence. Since most are Mom and Pop operations they depend on quality and cleanliness and when you mention its for a reef they fall all over themselves to help you out I have found.

 

[mcarroll]

I was gonna ask why you were switching if distilled was working out? There is not a huge diifference between RODI and distilled as far as your tank is concerned....and change for changes sake is kinda out of step in a nice, stable reef. If there's good reason, go ahead tho.

BTW, pure water almost doesn't have a pH of its own from my limited understanding, but will register about a 7 in a test. (Theoretically, absolutely pure water is an exact 7, but keeping water that pure is very hard.) It will sway - maybe dramatically - with the addition of anything....and pure water will dissolve everything. CO2 from the air, etc...everything...until an equillibrium is reached. Then the water will reflect that in the pH.

So I would hope to see a pH around 7, but it could definitely be higher or lower for good reason. (I don't know anyone who monitors the pH of their RODI water, so I have no idea what typical real-world numbers might be.)

-Matt

 

[AZDesertRat]

You cannot accurately test the pH of ultrapure waters. It means nothing and tells you nothing since there are too few ions to measure.
The only tests that mean anything are conductivity or TDS, nothing else has any level of accuracy in pure water and takes very expensive lab grade equipment and environments, this is why everyone is reporting troubles with the Hanna Checkers and phosphates, same deal, they do not work well on RO/DI.

 

[Rob in Puyallup]

Thanks for the input!

I've read a number of articles that recommend using RO/DI water, guess I was assuming that the two went together.

Think I'll stick with distilled, it hasn't caused any problems with the corals or the other critters, all looking and acting healthy and are growing well.

Thanks again!

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[navila06]

RODI and Distilled water is the same thing, the only difference is the process to get it to zero TDS. Do not use RO unless you know for sure what is left in it, stick with the distilled or RODI.

 

[AZDesertRat]

Distillation can possibly leave some volatiles that do not get removed and travel with the steam then are condensed back into the treated water. Its not much if any with a good still and quality control but I place distilled one step below good RO/DI on the quality scale because of that. My preference is always having your own RO/DI system so you alone control its quality and maintenance schedule but a good LFS should have RO/DI at a decent price.

 

[CJBROWN]

SW desert has pretty hard water, makes it harder to purify. Here in So-Cal water comes out of the tap at about 350ppm TDS. Yikes. A RO membrane knocks it down to about 30. When my DI cart is new it will put out 2-3 TDS and then gradually increases 'till it's obvious the DI crystals are not working anymore. I'll use water up to 20ppm, doesn't bother the tank. After that I put a new $25 DI cart in there.

For $160 or so a decent 35-40gpd RO/DI unit is worth hooking up. I did that a couple of years ago when I got started and it's worked out great. Put a 35gl barrel on a stand in the garage with a spigot, mix 5gl of salt mix at a time for bi-weekly water changes for a 75gl reef.

I will only use Corallife salt mix. I had a LOT of problems in the beginning using an inferior grade mix. My reef water consistently stays at 450-470ppm calc. Auto top-off is with kalkwasser. Corals grow like weeds.

 

[AZDesertRat]

A RO membrane should take the 350 tap TDS down to maybe 5-7 at the most if it is doing its job. My tap in Phoenix is 550+, my RO only TDS is between 2 and 3 and the membrane is over 5 years old. If your is 30 you definitely need a new membrane, thats only about 91% rejection rate and it should be 96-98%. For every 2% you increase that rejection rate you will double your DI life so imagine how much 0 TDS water you could get out a 98% efficient membrane. There is absolutely no reason to use RO/DI water with TDS any higher than 1 or 2, none at all, and a new DI cartridge should give you 0 TDS easily.
Remember, things like nitrates, phosphates and silicates are weakly ionized and do not register well on a TDS meter. When resin nears exhaustion, even before is shot, it starts to release those weakly ionized substances at much higher levels than it was in the tap water so you could be doing harm and not even realize it until is accumulates in your reef.

 

[Rob in Puyallup]

Hummmm. Don't know if I should believe the jug my "distilled" water came in or my TDS meter. I tested the water in the jug and the meter said "245". The reef tank says 999.

I'd expect the latter, I'm thinking. Not happy with the former.

Sometimes it's best not knowing.

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[Ron Reefman]

Sometimes it's best not knowing.

That's way too often what causes tanks to crash... not knowing. Learn all you can, it's a big part of this hobby!

 

[NanaReefer]

Hummmm. Don't know if I should believe the jug my "distilled" water came in or my TDS meter. I tested the water in the jug and the meter said "245". The reef tank says 999.

I'd expect the latter, I'm thinking. Not happy with the former.

Sometimes it's best not knowing.

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You cannot use a TDS meter on salt water, fresh only. If your getting that high of a reading from your distilled then it's either terrible water or your meters broke.

 

[AZDesertRat]

The TDS of saltwater is somewhere between 32000 and 35000+, your meter goes to 999 and some have a high range that reads to 10000 by tens.

Rinse, rinse,rinse your meter!!! You do not want saltwater deposits to contaminate and ruin the TDS probe. Use distilled or RO/DI water and rinse the heck out of it.

What meter do you have and is it calibrated?

 

[Rob in Puyallup]

I noticed that about the meter and saltwater. Lots of dissolved stuff in it like I expected.

I'm gonna check a different brand of distilled. May end up buying water from the reef shop.

This is the same distilled brand I've been using since I set up the tank, so I guess it may be the meter.

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[Rob in Puyallup]

Hey Rat,

The tds meter was a $30.00 "cheapie" from the LFS. Not sure it's calibratable, if that's a word.

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[Ron Reefman]

Hey Rat,

The tds meter was a $30.00 "cheapie" from the LFS. Not sure it's calibratable, if that's a word.

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Even cheap TDS meters work just fine. I've never seen one that can be calibrated (and I've seen dozens), but that doesn't mean there is no such an animal out there... but you don't need it. Borrow a friend's meter or go to your LFS and compare your's to their's when testing their RO/DI water before you buy it!