RO/DI water vs. Distilled side-by-side phosphate test

[Mike02]

I did a side-by-side phosphate test with RO/DI water i obtained from the "Marine Scene" LFS in Herdon, VA and Crystal Lake Distilled Water i obtained from a Rite Aid store. Although the test colors were similar, i actually got a lower phosphate reading with the Distilled water from Rite Aid. I estimate the Distilled water at 0.05 ppm and the RO/DI water at 0.10ppm. I used a Red Sea test kit and did one side-by-side test. Now i dont believe all the hoopla about RO/DI water. i dont think its all everyone cracks it up to be. The only good thing is that if you have a big tank, it would really be convenient to have a filter unit in your household.

 

[JennM]

Ask the store how old their RO membranes are. We regularly test the phosphate levels of the water emerging from the RO unit where I work, and they are 0. Of course we change our cartridges regularly too.

It could just be that the RO unit in question's cartridges are exhausted, and letting phosphates through.

Jenn

 

[SPC]

Mike, there are many variables here with your RO/DI sample.
1. Was it truly RO/DI or just RO?
2. How old were the membranes that were being used?
3. How many stages did this unit have?
4. What type of membranes were being used?
A local LFS sells what they call RO/DI water, but I was in the back one day and saw the unit, it was a drinking water unit from Home Depot.

Steve

 

[Kalkbreath]

I dont think any one has ever said that distilled is not a cleaner source, If you can afford distilled use it, ?

 

[SteveP]

Check that distilled water for copper too. Depending on how it's distilled, there may be a lot in there!

Steve
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[Mike02]

Steve, i never checked the distilled water for copper but i have been using distilled water for my tank since i started 2 months ago. I have nothing but corals and now a peppermint shrimp. the shrimp i got to get rid of the aptasia. but everything is healthy. if there was any copper in the tank it would have been instant death for the shrimp and probably the corals too. there are also plenty of amphipods and bristleworms in my tank.

 

[jdeets]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by Mike02:
<STRONG>Steve, i never checked the distilled water for copper but i have been using distilled water for my tank since i started 2 months ago. I have nothing but corals and now a peppermint shrimp. the shrimp i got to get rid of the aptasia. but everything is healthy. if there was any copper in the tank it would have been instant death for the shrimp and probably the corals too. there are also plenty of amphipods and bristleworms in my tank.</STRONG><HR></BLOCKQUOTE>

Mike--I'd recommend that you go ahead and check the distilled water for copper. The reason is that copper in trace amounts may not harm your inverts. Of course, the threshold of toxicity is VERY low. If your distilled water contains trace copper, then as you top off for evaporation, the copper concentration will gradually rise (since the copper ions would be left behind as water evaporates). Even if you haven't had any ill effects to date, you could in the future, if there is any in the water.

Just my $0.02.

 

[NaCl-H2O]

Actually MOST distilled water will read 0 sometimes there is a trace, RO/DI frequintly reads 0 or very close, DI water also usually reads close to 0, and reguler RO water will have some phosphates. It's a lot lower than tap but to much for most systems. MOST distilled water these days IS NOT ditilled in copper pipes, but it's a good idea to check just in case. I've been using distilled for 5 years now with no copper or phosphate problems. It's the cleanest and one of the cheapest types of water availible.

 

[pez]

If I remember properly, isn't the rejection factor for phosphate about 50% for RO units?
Or was that Si?

FWIW, I think the MS uses a 4 or 5 stage RO/DI unit. I know it is DI, I just can't remember if it is 4 or 5 stages.

-T

 

[Len]

pez,

it's Si. R/O membranes have a PO4 rejection rate of over 99%.

BTW, distilled water will remove almost all compounds and elements, including copper. The reason for the copper concern is that some distillation machines are built of copper that may leach minute concentrations back into solution.

 

[Anonymous]

As you discovered not all distilled water and not all RO water is the same. If you are buying RO/DI from an LFS ask them to prove that it it worth buying, have them at least run a PO4 test if not a Silicate test too. They should both be zero.

Our RO/DI registers zero phosphate with Salifert, Tropic Marine and FasTest kits. OTOH I have had a customer bring in distilled water from one of our local trauma centers and it was off the scale greater than 5ppm phosphate. He was better off using tap water.