The problem with using tap water is you would never know completely what's in it. Tap won't instantly kill or crash your tank. But there will be a huge possibility of metals and chemicals building up in your tank. Ang habol pa naman natin sa tank ay control sa parameters nito.
Here's our tapwater analysis results
https://www.google.com/url?sa=t&source= ... iR_ICyXHgQKung mapapansin niyo walang specific values na nakalagay.
Eto naman yung standards na ginagamit nila
https://www.google.com/url?sa=t&source= ... 39zRLl3i8QSo kung mapapansin niyo, masyadong mataas yung maximum allowable values nila para sa purpose natin. Check the values on Nitrate, Nitrite and Copper.
May bonus trace pesticides and chemicals pa.
Other references
https://www.google.com/url?sa=t&source= ... cxyO_7EJaghttp://www.nast.ph/index.php?option=com ... 1&Itemid=7Aside from the usual nasties, if your house has old piping, you risk contaminating the water with heavy metals like lead and copper. Free copper ions will kill corals... even fishes at high amounts.
More reading
http://www.advancedaquarist.com/2004/1/chemistryShould you use tapwater, at least have it prefiltered with a sediment filter inset and a carbon block.