RO old aquarium water

[Markp2483]

I was watching a koi YouTube channel from the uk.  One of those channels where they have massive square ponds with large viewing windows and crazy filtration. This guy water came from the towns water supply. For water changes he used RO water. The best RO are only about 1:1 so for every gallon of ro you have a gallon of waste.  You can imagine his water bill was getting pretty high on a 5000gallon pond.  So one day he plugged his ro into the pond.  He had to add a better pre filter but  he was able to reuse half the water that would normally go down the drain during water changes.  This got me thinking does anyone do that in the aquarium world?

I live in drought prone California. Thought it was kind of interesting option to conserve water.

[Tihshho]

Based on the setup required to do this, I personally wouldn't for my setup. I do use a decent amount of water, but to get a storage vat large enough for old water, a pump to get the adequate pressure to run the RO/DI system it just didn't make sense. If you're talking thousands of gallons, I'm sure this is something to consider. In terms of smaller aquariums, not so much. If you're worried about the waste water from the RO unit, you'd be better off having a storage container for the effluent and use that for other things rather than pipe it to a drain. 

[Markp2483]

I was thinking of a no storage option. Stick the ro intake into tank. Half the water goes back into the tank and half goes out to flower beds. Only have to replace half the water. Say you have 100 gal tank and do 50% water change. If you used ro water that’s 100 gallon waste (50 in effluent and 50 water change).  If you used an ro filter for water changes (25 gallons would be effluent from water change and 25 would be from effluent from new water) still a savings of 50%.

My tap water isn’t too bad in the 250 tds range but if I only do a 20% water change once a week it will get into the 400 tds range eventually and I do notice difference in shrimp breeding and general fish behavior.  
 

what I’m considering is use the ro filter just for water change and replace the remaining with tap water. This would be a 50% saving. But then maybe since my tds isnt creeping up as much maybe I could get away with a smaller water change which would increase my savings over doing large water changes once a week.

the biggest problem is finding an ro filter that can process water fast enough that your not spending days doing water changes which would be silly. Or maybe this is better setup for a slow continuous water change system. 

 

 

[Brian]

I’m not sold on this idea.  I have pretty good RO/DI unit.  
01.  Isn’t there efficiently related to water pressure?

02. Mine removes everything, but wouldn’t you want something in the water?  Mine says on it do not consume on a regular basis.  We (fish) need some minerals?

03. If are just going to target ammonia, nitrates and nitrites couldn’t you use more plants?  
 

I don’t know….  I guess I have some reading to do.    Thanks 

[Markp2483]

On 5/29/2022 at 4:09 AM, Brian said:

I’m not sold on this idea.  I have pretty good RO/DI unit.  
01.  Isn’t there efficiently related to water pressure?

02. Mine removes everything, but wouldn’t you want something in the water?  Mine says on it do not consume on a regular basis.  We (fish) need some minerals?

03. If are just going to target ammonia, nitrates and nitrites couldn’t you use more plants?  
 

I don’t know….  I guess I have some reading to do.    Thanks 

Hi Brian

yeah still just a thought experiment if it even makes sense. But to answer your questions 

 

1) yes would need a pump to pressurize the ro membrane.

2+3) yea not trying remove everything and I do like plants.  Nitrate is rarely an issue. I have hard water and I do need to add ferts as the plants show deficiencies if I don’t .  So my main reason for water changes is to remove the other stuff that builds up from evaporation.  Say my water had a tds reading of 500 and I find for my water the fish and shrimp like below 250tds from observation.  And it’s a 100 gal tank. The tds out of the tap is 150. 

without ro
Day 1 I do a 50 percent water change my tds drops from 500 to 325

day 2 do 50 percent water change and tds drops from 325 to 237.5

so after two water changes I use 100gal

with ro

day 1 do 50 percent using ro. 25gal is waste and 25gal goes back into the tank at 0 tds. Add 25 gal back from tap. Tds drops from 500 to 287.5

day 2 do the same . Tds drops from 287.5 to 181.5 

so this would be 50% water savings 

but you could take this further

Day 1 do 40% water change with ro. 20 gallon waste and 20 gal 0 tds back into tank and 20 gal from tap. Tds goes from 500 to 330

day 2 do the same 40% with Ro. Tds drops from 330 to 228.
40 gallons of waste and a 60% water savings over non ro water change

 

this is not for everyone.  But maybe a good solution for people in drought prone area like here in Southern California.

 

 

 

 

[Tihshho]

I still personally believe you might be putting the cart before the horse on this. Getting an RO unit and storing water and effluent is a ton cheaper than going the route you propose.

You've already mentioned one of the key things about RO units and it's production of gallons per day. To make this unit fast isn't cheap, and to make the unit cheap means it isn't fast. By the time you're done setting this up you might have invested more than what you expect in terms of a water bill. I've seen some people setup collection of effluent water (specifically Californian's) to be setup for non potable water useage. Specifically, a lot of Reef folk do this and use the effluent to feed to their toilets as well as to water their garden.

Another issue that's been brought up is remineralizing. To set something like this up more than likely would be automated, which means you'd need to automate your remineralization process. This is another additional cost. 

Another thing to keep in mind is that source water that goes into an RO unit generally doesn't contain particulates, so booster pumps generally last a long time if they are required to get to the nominal pressures required. If you plan on pumping and boosting the water, you need to have a series of prefilters that will catch the particulates out prior to getting to a booster. These filters would need to be maintained in an extreme regular fashion in order to not restrict the flow to the booster pump, otherwise you will burn up the pump or not get adequte filtration through your RO membrane. 

[nabokovfan87]

Sidenote. Netflix show travelers discusses this topic.  Very fun show.  Hit's a little close to home now because of the past few years, but they run into a situation where they RODI'd the water so much that you couldn't clean it anymore.

On 5/30/2022 at 8:37 PM, Tihshho said:

You've already mentioned one of the key things about RO units and it's production of gallons per day. To make this unit fast isn't cheap, and to make the unit cheap means it isn't fast. By the time you're done setting this up you might have invested more than what you expect in terms of a water bill. I've seen some people setup collection of effluent water (specifically Californian's) to be setup for non potable water useage. Specifically, a lot of Reef folk do this and use the effluent to feed to their toilets as well as to water their garden.

Another issue that's been brought up is remineralizing. To set something like this up more than likely would be automated, which means you'd need to automate your remineralization process. This is another additional cost. 

The remineralization might overlap into coffee making territory and there might be some industrial machines / designs to handle this.  I definitely approve of using the waste elsewhere, but again.... beware of the whole travelers concept and what that slippery slope leads to.