Filling new 315g system for first time.

Eder · Feb 6, 2019

Wife and I relocated and upgraded tanks. We have several years of experience and this 315g system will be our third. Its just about ready to move into the house and fill up!!!

This may sound like a stupid question, however, whether where we live now is outrageously expensive. $120 buy in a month for 2500g and $100 for every 1,000g over.

So, was curious if there is absolutely any way we can get away with not wasting tons of water through our RODI and filling it, treating the water, letting it cycle, then introducing our fish/coral once ready.

Thoughts? Or am I just going to have to pay like $300 to fill up my new tank?

Matthew Frost · Feb 6, 2019

I have often wondered if I could store RODI waste water and pump it back through my RODI system a second, or even third time.

Adalius · Feb 6, 2019

You can. But you're going to get diminishing returns. Think about it this way, using made up numbers and some suspension of the exact mechanics. You have 3 parts of water with, say, 100 tds, you output 1 part clean water with 2 tds, the rejected garbage from that 1 part ends up in the 2 parts waste water, so now the tds in them is something higher, like say 250 tds. Now you're going to run that through the filter, you get the same 98% rejection rate if the pressure is the same, so now you're outputting 5tds water and 350+ tds water. Run that through, now you're getting 7 tds water, etc etc. Sure the DI resin might keep it so the end result is still close to 0, but with every pass you're also using up your resin faster since you're pushing higher and higher TDS water through it.

IDAN · Feb 6, 2019

Eder said:
Wife and I relocated and upgraded tanks. We have several years of experience and this 315g system will be our third. Its just about ready to move into the house and fill up!!!

This may sound like a stupid question, however, whether where we live now is outrageously expensive. $120 buy in a month for 2500g and $100 for every 1,000g over.

So, was curious if there is absolutely any way we can get away with not wasting tons of water through our RODI and filling it, treating the water, letting it cycle, then introducing our fish/coral once ready.

Thoughts? Or am I just going to have to pay like $300 to fill up my new tank?

I had slimier problem with my 200 total volume, at the end I went to my LFS and bought all the water, it was cheaper, easier, and I didn't have to buy extra filters for my RODI system (yet).

Eder · Feb 7, 2019

Adalius said:
You can. But you're going to get diminishing returns. Think about it this way, using made up numbers and some suspension of the exact mechanics. You have 3 parts of water with, say, 100 tds, you output 1 part clean water with 2 tds, the rejected garbage from that 1 part ends up in the 2 parts waste water, so now the tds in them is something higher, like say 250 tds. Now you're going to run that through the filter, you get the same 98% rejection rate if the pressure is the same, so now you're outputting 5tds water and 350+ tds water. Run that through, now you're getting 7 tds water, etc etc. Sure the DI resin might keep it so the end result is still close to 0, but with every pass you're also using up your resin faster since you're pushing higher and higher TDS water through it.

Wonder if I could just run my waste water back in line and use it as you say. I won’t have 100% filtered water but I can get bulk DI resin and change it often?

Can also change filters 2-3x throughout the initial fill up?

I recognize wholeheartedly this isn’t ideal and won’t be 100% water quality but we’re talking about $75ish to fill up vs $4-700

I could go to LFS. But we’re a tad far now from it. I only have six 5 gallon jugs.

Say I even go get cheap buckets from one depot and end up with 12. I’d have to drive approx 26x to store. Not a viable option for me at all.

This would be a one time event ever. After initial fill I would then filter water with RODI and not use the waste water at all.

Thoughts?

Adalius · Feb 7, 2019

Maybe I'm not following something here, but you say your first 2500 gallons is $120, and each 1000 after is another $100. With that, I'm not sure why you think it's going to cost you $4-700 to fill it in the first place. You'll probably hit the minimum threshold just with your normal household use, so consider the first $120 mandatory. After that you'd use, with just a single pass and a 4:1 ratio 1500 gallons or so to get your tank filled. You said above that's only $100 per 1000g over, so you'd only be out $150 to fill it. Where are you getting $400-700 from?

Also, don't forget you can use the waste RODI water for other things too to save usage. You can use it for watering the lawn/plants, cleaning dishes, cleaning clothes, etc. I would imagine if you got creative you could probably booster pump it to a washing machine or dishwasher even. Any of those uses offset the cost you would have from using more fresh tap water for whatever.

Anyway, just for giggles I did the math. Presuming you get a 1 : 2 :: clean : waste ratio, which is better than even a water saver cartridge would normally do, the math follows a nice sequence. After the first pass, you have a 1:3 ratio of clean : total water. After N passes, you will have a ratio that approaches 1:1 (which makes sense, since you are cleaning the dirty more and more). The ratio for a given number of passes (N) is in the form f(N-1) * 3 + 2^(N-1) : 3^N. f(N-1) is the left side of the ratio for one less pass. If we then solve these ratios against x for 320 gallons output, we see that with 1, 2, 3...10 passes you need to supply : 960, 576, 455, 399, 369, 351, 340, 333, 329, or 326 gallons, respectfully. Now granted this makes some serious presumptions, like that you can maintain 1:2 ratio. It also presumes that you can push sludge through a filter, because your TDS is going to be insane after even a few passes since you're concentrating it in each waste pass. Some people around here have posted their TDS at the tap and at the waste stream, after one pass 150 TDS tap water in comes out as 250 TDS waste water, as an example. In any case, doing any more than about 3-4 passes would be pretty fruitless since you're doing a lot of extra work for not a lot of gains. If your filter isn't close to that ratio, you can gain a few more passes, but not many. A normal 1:4 filter, without running the math, is probably going to run about 6 passes before the returns aren't worth it.

Still not sure I'd recommend this, but if you're willing to burn through some resin and a filter, I guess that's your decision.