What are the differences?

[divecj5]

First off, thanks for the wealth of information that I have read here thus far. Although I don't have a tank yet, I have been reading just about EVERYTHING that I can about SW tanks and I am trying to get a good gameplan together before jumping in feet first.

Just so you all know, I am looking to start a 55 gallon FOWLR. I am planning on having a 3-5 inch sand bed, about 30# of cured rock to start off with, and a Coralife Super Skimmer (the one rated to 125 gallons). Although I am looking to only have live rock at this point, I'm sure that I will want to inlcude some soft corals at some point in the near future so I might go ahead and see about upgrading the lighting from an Eclipse NO hood to something more substantial.

Now that you all know that, I am just a little unsure about the main differences between RO/DI filtered water and water from say a Pur or Brita filter. I understand the main premise behind the two (Pur/Brita are basically carbon filters) but what is the main difference in the resulting water? If I have pretty decent tap water to begin with with a low amount of total dissolved solids, is a 3 stage Brita/Pur filter sufficient? Is it just that the RO filter will filter out smaller impurities than the carbon filter?

I'm just curious and trying to finalize a good gameplan of what I still need to purchase and all that good stuff. Thanks in advance for any and all suggestions.

Adam

[Amphiprion]

The main difference in the product water is a simple matter of purity. RO water, on average, is going to be much purer than water filtered through a carbon filter. Most RO units already have a carbon filter, after which, the water is filtered further. If you believe your tap water is suitable, simply get a TDS meter (or borrow one, temporarily) and verify it. In any case, it would be best to buy one of these meters so you can keep track of the water purity. IMHO, I would not use any water above 10 ppm total dissolved solids--most tapwater (even good tap water) is higher than that. I have very soft water where I live, but it still comes to about 60 ppm tds.

[MCary]

To really understand you need to know the nature of water. Water is the universal solvent. When exposed to water acids, salts and many metals go into solution. Carbon works by means of physical adsorption, that is physical adsorption occurs because all molecules exert attractive forces, especially molecules at the surface of a solid (pore walls of carbon), and these surface molecules seek other molecules to adhere to. The large internal surface area of carbon has many attractive forces that work to attract other molecules. Contaminants in water are adsorbed (or held) to the surface of carbon by surface attractive forces similar to gravitational forces. Water contaminants adsorb because the attraction of the carbon surface for them is stronger than the attractive forces that keep them dissolved in solution. (Chlorine is also removed by carbon but chlorine removal from water involves the chemical reaction of chlorine with carbon to form chloride ions.)

Compounds that are more adsorbable onto activated carbon generally have a lower water solubility, are organic (made up of carbon atoms), have a higher molecular weight and a neutral or non-polar chemical nature.

This leaves alot of stuff. Salt, alot of metals, calcium, inorganic phosphates, etc.

The way an RO system works is that the membrane only allows unbound H2O molecules through. Those bound with salts and metals are too big and collect on the outside of the membrane where they are flushed off by the waster water, which is 80% or more of the water entering the system. What does get through are mostly ions which are collected by the resins in the DI canister. The water that comes out should be almost pure. In the lab we call pure water reagent grade.

So summary, brita water, just filtered tap water, not pure.
RO/DI close to pure water.

Mike

[divecj5]

Awesome...thank you both for the great explanations. It now makes complete sense and I will definiltey move on from here. Thank you for the time and effort you put into the explanations

Adam

[hawaiianwargod]

divecj5
[welcome]