Reverse Osmosis - Really Dumb Question - Why Tap Water?

[AsleepInYorkshire]

Hi

I've been working on a little set up to automatically empty and fill two freshwater aquariums. I've managed to design a system using one RO unit refilling directly into the two tanks and it's designed to change 50% of the water per week but on a daily basis.

Our tap water isn't the best. It's average 10ppm nitrates and over 1.8ppm phosphates. I've managed to set up filters which can bring the nitrates in the tank down to 1ppm. But the level of the phosphates is "nattering" me. Hence the use of RO water.

The design will use our tap water passing through the RO filter before entering the fish tank.

In simple terms this is the way it will work

1. Small pumps in the tanks will be automatically turned on daily to empty a small amount of water to waste pipes
2. Flood guardians will open solenoid valves and allow RO water direct from the filter into the tanks. When full the Flood Guardian will close the solenoids.
3. The pumps will come on at different times and probably between 1 to 3 times a day (dependant upon a few variables I've still to work out)

So my really dumb question is this.

Why do I need to bring the new water in from the tap? It genuinely seems counter intuitive as the tap water is the source of the problem in the first place. I appreciate it's a bit of a radical thought but why don't I just use the water coming out of the tank and put that through the RO unit?

I appreciate the water would need to be mechanically filtered first and I "think" that could be achieved by using a cannister filter with no pump - some of you may call it a "booster" filter. Essentially it's a cannister with mechanical filters inside. Then there's the issue of the RO waste water. I "think" this could just be sent back to the tank.

Noting finally I still have a completely separate system to deliver new water should it be needed. But as I've said that feels like putting the fox in charge of the hen house.

Has anyone tried this at all and if so what results did you get?

Thank you

AiYn'U

 

[MomeWrath]

Putting the wastewater from the RO unit into the tank would completely defeat the purpose, I think, since you would be adding back all the junk you just filtered out...
Have you got a plan for dechlorinating the incoming water, or are you on a well? What about remineralizing the RO water?
Have you considered a phosban reactor to solve the phosphate issue?
Sounds like a recipe for a bangup planted tank, in my opinion!

 

[AsleepInYorkshire]

Putting the wastewater from the RO unit into the tank would completely defeat the purpose, I think, since you would be adding back all the junk you just filtered out...
Have you got a plan for dechlorinating the incoming water, or are you on a well? What about remineralizing the RO water?
Have you considered a phosban reactor to solve the phosphate issue?
Sounds like a recipe for a bangup planted tank, in my opinion!

I've not thought about a phosban reactor no. Is it more like a phosphate filter? The only reason I am considering the use of RO is to remove the phosphate. The remineralisation was something I had planned to do manually. The tank is quite heavily planted and has Co2. The plants are in a growing medium, albeit I don't think it's a brilliant medium as it seems more "mainstream". My best guess is our tap water has phosphate levels in excess of 2ppm and it's limiting the time we can have the lights on to 2-3hrs a day. So the plants are growing but quite slowly.

AiYn'U