Calling it tap water for this type of use is barely accurate. Calling it "mystery water" would be more accurate. While there are some very lucky people who have had their water tested and have crazy low TDS and may be okay with it, the majority of people using mystery water do so because either they don't care or don't know any better.
In 2005 I filled my nano reef with tap water and got a huge algae outbreak. For 1 week I bought RO water from the grocery store. Since I've used RO/DI always. I later learned the water was typically 175 tds out of the tap. At my current house the well water is very clean at 50-55TDS with a DI lasting close to a year despite making a ton of water.
Do you use tap water for ATO - do you have a cover on your tank (to slow evaporation)? I tend to agree with you - I have Stendker discus - and to do water changes - I drain 75 percent of the water from the tank - take a hose from my tap - and fill the tank (adding the conditioner periodically) - and have never had an issue. For my saltwater tank - the I use RODI - I guess I would consider that you are 'lucky' in the water you have. The point is - using RODI - there can be no 'disadvantage' - right? But - others have had problems with tap water - especially when - unexpectedly - the water company triples the chlorine - or chloramines - because of some outbreak. In theory - the Tap water has 50-100 TDS (PPM) - sea water has >10,000 TDS (PPM) - so whatever you're adding with tap water - you're right - it will be smallEhh you sound like some dis us freak in my area who obsess over tds. SOME people do rodi some dont.. and Discus hans in baltimore has the best discus in the country and he uses tao water.. Tons of locsl breeders here breed in tap water. And ive taken corals bleached and looking like crap in tanks with rodi in northern va and they explode in my tank.
And my tank uses tap water.. it isnt about (not caring) and not knowing better. Its more that i cant fill 70 gallons of rodi on a 3rd level townhouse in a trash can. I mean where am i going to store this trash can on a 3rd level ? Sure maybe if you put your tank ina chilly basement or pipe it up 3 levels.. but for me thats deff not feasable. Nore am i having a trash can in my upper level connecting my sink running hoses from my bathroom to the can..
Tap works just fine. I havent not met 1 coral i cannot grow yet. And i have some high end sps and acros.
I think youre pretty ignorant for that comment tbh.
Also algae can be controlled by the proper fish and cleanup crew and uv sterilizers. tanks also go through algae phazes. I had the diatom. Green hair algae. And brown stringy algae explosions. But after 5 months of it being controlled with tangs. Algae eating fish of various kinds. And snails and urchins and so forth. I cant even grow algae anymore.
My tank is 2 years old and i gatta HAND feed my sea urchins due to not being able to grow any kind of hair or diatom or anything. My rocks have their biofilm on them now and nothing else can grow on them.
And guess what ... i do 50% water changes with tap water a month.