my water parameters, do i need a RO?

[Pufferpoison]

ok here's my water parameters out of the tap:

Ph 7.8
KH 286 ppm
GH 161PPM
and i have never had an algae problem, until recently i had a speck of brown algae and have 5 tanks running, so i was told that my tap water must not have much phosphate in it. i'm going to go with a 90G reef tank and wanted to try and avoid a RO. i don't have a way to test calcium yet, but how does these figures look so far for tap water?

 

[RENEGADE]

don't forget that tap has chlorine and floride and copper and rust in it

 

[Crown Royal]

Tap water varies greatly from location to location. The parameters you cite are next to irrelevant when it comes to SW since your salt mix will properly buffer the pH/KH/GH in any event. It's things like copper and other heavy metals, phosphate and nitrate which will screw up your reef. It is impossible to deal with these contaminants 100% of the time even if you have generally high quality tapwater because all it takes is the water company messing around with the pipes outside while you do a water change to vastly alter the tap water's chemistry and kill everything. Many people run successful reefs without RO/DI water but it comes down to this (IMO): you've already spent big $$$ and effort setting up the reef, an RO/DI unit is good simple insurance against disaster as you know exactly what's going into the tank.

 

[Pufferpoison]

i bought a copper and phosphate test kit and checked the tap water, results:

Copper 0 - stayed clear didn't change at all
Phosphates .50
i used the tube test kits from aquarium pharmacitucal.

this is good right?

 

[Crown Royal]

0.5 ppm of phosphate out of your tap is not a huge amount but enough to be a concern if you're adding it to your reef tank every time you do a water change.

There's also nitrate and a lot of other stuff you can't test for that may be present. The easiest way to get an estimation of how much "stuff" is in you tap water is a TDS (total dissolved solids) meter.

If you plan on having a reef in the long term, your safest bet is to invest in a good RO/DI system.