75 vs 100 RODI unit

[nunlef]

sorry about adding another rodi thread, but I didn't want to hijack anyone's thread.

I'm guessing my unit has run it's course because I figured out the source of my 100ppm nitrate test.... yep my filtered water.

Anyway, the unit I have was just a cheapy ebay model (only 60 including shipping), so I will be buying a new unit this weekend. I went to Air water and Ice, and they have the option of 75gpd or 100gpd membrane.

My question, is one superior in water quality? I ask because I can't think of any other reason someone would go to a smaller gpd output unless less is better.

Thanks

 

[DaveK]

Some people claim that the lower output units produce water with a lower TDS reading. Personally, I have never seen this.

The point is somewhat moot because after the water comes out of the RO unit you are going to run it through a DI unit anyway. Bottom line is that even if the 100 GPD unit let through a little TDS, all that would happen is that the DI cartridge would get used up a little faster.

 

[nunlef]

that sounds reasonable. Thanks, a 100gpd one for me, then.

 

[MikeinToronto]

sorry about adding another rodi thread, but I didn't want to hijack anyone's thread.

I'm guessing my unit has run it's course because I figured out the source of my 100ppm nitrate test.... yep my filtered water.

Anyway, the unit I have was just a cheapy ebay model (only 60 including shipping), so I will be buying a new unit this weekend. I went to Air water and Ice, and they have the option of 75gpd or 100gpd membrane.

My question, is one superior in water quality? I ask because I can't think of any other reason someone would go to a smaller gpd output unless less is better.

Thanks

The DOW 75 gpd membrane produces a better ratio of good water to waste, ie: the 75 gpd membrane is more efficient.
The amount of water you use dictates the size of your membrane. With 75 vs 100 there may not be that much difference but to use a more extreme example, you wouldn't want to use a 100 gpd unit if your tank is only 30 gallons. You would probably opt for a 50 gpd unit. It doesn't mean you can't use the 100 gpd unit, it just means you have to run water through it regularly that you won't use and waste this.

A 75 gpd unit is the exact same as a 100 gpd unit. The only difference is the membrane and the flow restrictor so don't beat yourself up over the decision. A flow restrictor should be changed every time you replace the membrane anyway so pick the size membrane you want and if you don't like it, pick the other size in 5 years when you need to replace it, lol.

 

[nunlef]

I have a 120g dt and 30g sump (though this week I'm prob going to updgrade to a 54g bin, pending husband's approval of fish room), so total water volume is roughly 110g, maybe upto 140g in the near future. I would guess the 100gpd membrane would still be my better choice. I will continue heavy water changes for the next couple of months since my tank is still VERY new (just set it up in january).

Now I'm wondering how long of a waste tube I can use.

Right now, I'm running waste water into buckets to be used elsewhere in the house (cleaning, water for other pets, etc). This summer I would like to divert waste into the gardens.

Does anyone have a setup that utilizes a hose or hose/pump combo that can run waste water a long distance? I refuse to run potentially useful water down a drain. It's potentially 120g per week through this summer.

thanks

 

[MikeinToronto]

I have a 120g dt and 30g sump (though this week I'm prob going to updgrade to a 54g bin, pending husband's approval of fish room), so total water volume is roughly 110g, maybe upto 140g in the near future. I would guess the 100gpd membrane would still be my better choice. I will continue heavy water changes for the next couple of months since my tank is still VERY new (just set it up in january).

Now I'm wondering how long of a waste tube I can use.

Right now, I'm running waste water into buckets to be used elsewhere in the house (cleaning, water for other pets, etc). This summer I would like to divert waste into the gardens.

Does anyone have a setup that utilizes a hose or hose/pump combo that can run waste water a long distance? I refuse to run potentially useful water down a drain. It's potentially 120g per week through this summer.

thanks

If you're concerned about throwing away water needlessly, you probably want a 75 gpd unit. Just to break it down, a 100 gpd unit produces about 4 gallons per hour while a 75 gpd unit produces 3 so there isn't much difference but the rejection rate for the 75 gpd is about 7% higher than the 100 (ie: the 100 wastes 7% more water).
After the initial fill up, you just need to do water changes and either unit will be large enough for this - unless you are draining your reservoir each time before refill.
If you want to improve your output even more you can add a booster pump to reduce the waste. This is useful on the 100 gpd membrane but I don't think you'll notice as much savings on the 75 gpd because it is already close to 100% (although there is still savings).
Some people are very adamant that no one use 100 gpd membranes for aquariums. For me water is cheap so I don't worry too much but I still use a 75 gpd membrane.

My waste water tube is 25'. As long as the tube is below the unit (gravity fed) you can have a pretty long tube. When I was filling my tank I had the whole unit stretched across about 50' from the laundry room to the living room (25' tubes on each side of the unit).

 

[nunlef]

well i just measured, and 25' will get me to a rain resevior barrel just outside the door. The unit will be mounted 2' from the water line, and only 4-7 ft (again pending fish room) fom the tank.

Thanks so much for your advice. I knew I could count on reefsanctuary people.