Why is DI of water recommended?

[Duchess]

Here's a newbie looking for an explanation of why I should purchase a RO/DI water unit rather than a RO. I understand the need for RO to remove "stuff" from the water. However, why isn't the RO sufficient for the fish tank? I appreciate any explanations you can give! Thank you!

[Limpit]

The DI filter just removes any leftover impurities left after the water goes through the RO filter. Basically more pure of water.

[JosephineAd]

I'm not real sure but I think RO can't remove phosphates but the DI can.

[aquaman67]

A RO is a mechanical filter. Water is forced though a semi-permeable membrane. Anything that is the same size or smaller than a water molecule can pass through a RO membrane. Some ions (atoms or molecules that have extra or missing electrons) can pass through the RO membrane. These ions have an electric charge. The deionizer uses this difference in charge to attract the ions to the media and only lets neutral molecules pass, most of which are pure H2O.

[Duchess]

Thank you for your replies -- I appreciate your input! While I can appreciate that the cleaner the water, the better, I'm wondering how the ions that make it through the RO can affect my tank.

[der_wille_zur_macht]

Certain contaminants - silicate comes to mind - will pass through an RO membrane at almost the same levels they were present in your tap water.

Check eBay - effective, high capacity, top of the line RO/DI units are selling for about $100 or so these days. I have a 6 stage, 110 gpd unit with a drinking kit (pressure tank and seperate tap above the sink) that I paid $115 for, shipped.

[Duchess]

Thank you for the recommendation -- I'll take a look on eBay.

[aquaman67]

Sorry, I guess I really didn't answer your question.

RO's are about 90% effective, give or take.

That still leaves 10% of undesireables in your water.

The question then becomes, why not just take care of the last 10% and know that you are using pure water?

Some people here use tap water and report no problems. I guess it's just a matter of how many chances you are willing to take.