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Old 12-21-2010, 05:10 PM   #1
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Just calculated how much to produce my own RO water

I've been doing some number crunching and came to some interesting conclusions that I thought could benefit some people who are getting into the hobby, like myself.

I've been reading and reading about how to setup my 65G tank and one thing that seemed to be general knowledge is that RO water is better to use than treated tap water. Will treated tap water work? For the most part. Will RO work? For sure. This of course requires either buying it from someone who makes it or buying an RO/DI setup. Option 2 seemed pricey to me so I found a LFS selling it. To my surprise they wanted .50 cents a gallon. To get my 65G going with sump water included would have been around $37.50 plus gas getting there and back. That's not even thinking about water changes that will be needed.

Next option was purchasing a RO/DI unit. I lucked out and found someone selling this SpectraPure unit on craigslist used for $50. I wanted something quick and they said filters were just changed a few months ago. I had a TDS test done on it to prove it was putting out 0ppm which it did. Anyways, on to the good stuff.

I checked my utilities bill to see what I'm paying for water. I'm paying $2.34 per 100cf for water and paying $3.80 per 100cf for sewage. Sewage is based off our water use. So I'm basically paying $6.14 per 100cf of water used. 100cf of water equals 748 gallons to put things in an easier measurement.

My water pressure at the RO unit is 76psi which helps a lot with efficiency. Water is cold this time of year so that doesn't help. After a few tests I figured that for every 1 gallon of good RO water I get I'm "wasting" 2.5 gallons. So basically it takes 3.5 gallons of water to make 1 good gallon.

748 / 3.5 = 213.714 gallons
213.714 gallons of good RO water costs me $6.14
$6.14 / 213.714 = 0.029 cents per gallon

So as you can see the per gallon cost is very minimal even including the "wasted" water. At this rate it will cost me $2.18 to initially fill my tank. To do a 10g water change will cost 0.29 cents. Doing that once a week for a year will cost $15.08. Even with the cost of replacing filters and membranes annual costs shouldn't be much over $50.

If I were to purchase RO from the LFS I'd be at around $260 doing 10g changes weekly for the year.

CONCLUSION: Even if you had to spend $200 on a new RO/DI unit it should pay for itself within the first year!
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Old 12-21-2010, 09:34 PM   #2
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Old 12-21-2010, 11:19 PM   #3
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Good explaination.....
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Old 12-21-2010, 11:25 PM   #4
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now calculate the price of salt into that! see how much per gallon it is, that'd be interesting to see how much i'm wasting on buying premade SW

(for a reef, if that matters)
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Old 12-21-2010, 11:39 PM   #5
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Well salt around here is 60ish a bucket which does about 160 gallons or so. Thats around .39 cents a gallon. That puts you at .42 cents a gallon or so.
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Old 12-21-2010, 11:47 PM   #6
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Also note that in *some* municipalities if you contact your water company they may opt to allow you a second water meter for the line that is not producing any sewage and not charge you for that on the second meter.
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Old 12-22-2010, 12:18 AM   #7
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I think that is why some people meter their hose bib water separately. However, you want your RO to feed from the softened water line so that doesn't work.

That is a very good breakdown of the cost. I think I generated about 2000+ gallons my first year and spent $115 for the initial system and bought about $150 worth of DI resin, valves, tees, and tubing so I think I'm way ahead of cost of buying straight RO water at $0.37/gal at Wal-mart.

As for salt, I get a 200g box of Reef Crystals for about $52 through a group buy at LFS whenever they have it, I can usually get it for $56 from Foster & Smith if I buy enough, but I mix it to Salinity 35 which is 3 cups for 5 gallons instead of 2-1/2 cups, so that's 0.6 c/g so I get about 165 gallons of SW per box, or $0.33/gallon plus your $0.03/g water is about $0.36 per gallon mixed up 35 Salinity saltwater.

I'm sure the LFS SW is not 35 salinity and probably not Reef Crystals either though...
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Old 12-22-2010, 10:01 AM   #8
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Thanks for doing the math on that. It illustrates the point perfectly.

I do feel compelled to ask you to up your PWC to 15 gallons/week which is closer (sump included), but just over the recommended 10% weekly.
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Old 12-22-2010, 10:33 AM   #9
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Great work with the calculations. I'd bet it would be even more skewed if you added in the cost of gas driving to and from wal-mart or to and from your lfs every week for water.
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Old 12-22-2010, 10:47 AM   #10
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New calcs based on actual salt costs and %15 water changes.

$49 (Red Sea Pro treats 175g from my LFS) = .28 cents per gallon + .029 for water = .309 per gallon for mixed water.

%15PWC x 75G = 11.25g per week

11.25g x .309 = $3.48 per week for mixed water
11.25g x .029 = .33 cents per week for RO water

$3.48 x 52 = $180.96 for annual mixed water cost
.33 x 52 = $17.16 for annual RO water cost
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Old 12-22-2010, 11:09 AM   #11
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+1 Rep bro! Awesome post... this should be a Sticky!
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Old 12-22-2010, 01:00 PM   #12
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Great post. Thanks for putting the numbers up for everyone to see.
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Old 12-22-2010, 02:05 PM   #13
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You have inspired me to screw around at work today.

I went through my water bills for the past year and added up all the water and sewer costs, fees, and taxes and came up with a total cost that varies between $0.0092 / gallon during high useage months (10,000 gallons - I have 4 kids) and exactly $0.01 / gallon during low useage months.

My system was advertised as having a 1.5:1 waste ratio, so I go through 2.5 gallons to make 1 gallon of water. Therefore, my high-end water cost is $0.025 / gallon.

For the reef I maintain, as I put in my last message, I can buy RC on Drs F&S for $55 and makes 167 gallons at Salinity 35, so that runs about $0.33 / gallon to mix, so my total cost is $0.355 / gallon. I don't do regular changes on that one though.

For the FOWLRs I maintain, I try to adhere to a monthly PWC of 40 gallons, because that is one BRUTE trash can full of water. The salt I use for that is Instant Ocean Sea Salt (not RC) and that's $48 on F&S and makes 182 gallons at Salinity 32 (an extra 1/4 cup for every 5 gallons, or a total of 22 cups), so that runs $0.264 / gallon. Total SW cost on that is then $0.289 / gallon.

So a 40g PWC w/IO-SS currently costs me $11.56.

If I was buying water from my LFS at $0.50 / gallon (I don't even know if any of them sell it around here), that would cost about $20, and like I said before, the salinity might not be 32 but probably 29 or 30, and you don't know if they started with RO/DI, RO, or tap water for that matter.

When my DI runs out, I am then forced to go and fill up buckets at the Culligan RO station at Wal-Mart, which costs $0.37/gallon. With that figured into the equation, 40g of IO-SS mix runs $0.634 / gallon, or $25.36. More than LFS, but I know what I started with and what I finised with. But, it involves a 1-hour round trip (including fill) to Wal-Mart, plus the extra hauling of buckets to the car, then into the house to mix it. So it's definitely not the deisred option.

Monthly cost:

WM SW Mix: $25.36
LFS SW Mix: $20
Home RO/DI SW Mix: $11.56

Monthly Savings:

Home savings over LFS: $8.44
Home Savings over WM: $13.8

Yearly Cost:

WM SW Mix: $304.32
LFS SW Mix: $240
Home RO/DI SW Mix: $138.72

Yearly savings:

Home over LFS: $101.28
Home over WM: $165.60

My conclusion: While purchasing an RO/DI system can range anywhere from $50-$400, and yearly replacement of media also varies (maybe $40-$80, maybe less), buying your own RO/DI system is really less about cost savings as it is about being in control of your system and eliminating all other potential variables. The time savings factor is somewhat offset, you either spend time going to the LFS or filling up buckets, or you make your own and then buy and mix the salt.

For a FO or FOWLR system, buying pre-mixed SW might be OK because you're a little less worried about the origin of the water, unless algae is a big problem and you have eliminated all other possibilities.

For a Reef system however, the cost of the RO system and media are grossly outweighed by the cost of potentially losing all your corals during a tank crash due to any number of possible unknowns related to water origin that is out of your control. Plus, since a reef should generally be maintained at higher salinity (and Calcium, Magnesium, etc) than a FO/FOWLR, you really should mix up your own SW (unless it's an all-softie tank and easy corals). IMO, an RO/DI system is a must-have for a full blown reef system.
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Old 12-22-2010, 03:19 PM   #14
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Originally Posted by Floyd R Turbo View Post
You have inspired me to screw around at work today.
Great post! I'm a bit nerdy and enjoy numbers so it's interesting to me to see how that goes. I think it's also very helpful to see monthly and yearly figures on upkeep like this. It really puts the cost of upkeep right out on the table!
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Old 12-27-2010, 10:35 AM   #15
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So has anyone dabbled in electricity costs for their tanks?

My approximate electricity rate is 11.6 cents per kWh. That means 11.6 cents per 1,000watts. That's 0.0116 per watt.

(4) 24" VHO bulbs - 74w x 4 x 8 hours = 2368 watts per day
Mag 9.5 - 93w x 24 = 2232 watts per day
Mag 7 - 70w x 24 = 1680 watts per day
(2) Kolaria 750 - 4.5w x 2 x 24 = 216 watts per day
300w heater - 300w x 12 hours = 3600 watts per day (just a guess, not sure how often the heater is on during the day)

Total = 10,096 watts per day. 10,096 / 1000 = 10.096kWh per day.

10.096 x 11.6 cents = 117.1136 cents per day

$1.17 per day
$35.10 per month
$421.20 per year
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Old 12-27-2010, 01:39 PM   #16
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Just a clarification on your units (I'm an electrical engineer, so I can't let it slide!!) your math is correct but the "watts per day" is really watt-hours per day...so 2368 watt-hours/day or 2.368 kWh/day. Other than that the only thing I can think of that you're missing is the ballast kWh which is probably on the order of 5-10 watts in addition to the lamps, plus any loss factor but you're in the ballpark...

The best way to get a read on it would be to have everything on it's own circuit and then clamp a monitor around the wires and have it record for a week and look at the average. But I digress.
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Old 12-27-2010, 02:23 PM   #17
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Thank you for that clarification! I definitely left that out and would make a difference technically. I even had the "hours" written out in the equation! haha

I was wondering about the ballast. Figured it would require something but wasn't sure what. My brother has one of those plug in meters, then you plug in your appliance to that and it will read usage. I wonder how accurate it is.
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Old 12-27-2010, 04:39 PM   #18
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It's probably pretty accurate. The ballasts don't really take up much energy, at least not on a standard recessed 2x4 fixture in an office environment. For old T12 fixtures we figure for every 2 lamps or fraction thereof requires 1 ballast (old magnetic type) that consumes 10 watts, so a 3-lamp fixture would need 2 10W ballasts. T8 electronic ballasts can go up to 4 lamps and only consume 5W. As for aquarium specialty lighting, I would say that a 4 lamp VHO fixture might consume as much as 15W but that's only a somewhat educated guess.

I see this is now a sticky...
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Old 12-27-2010, 05:11 PM   #19
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I see this is now a sticky...
Well that's surprising?

Back to the ballast talk though. I read that the icecap power factor is around 60%. Someone running (2) 39w T5s was actually pulling 2.12A at the AC outlet. How does that work? 2.12A @ 120v is around 254 watts right? Factor in that power factor and you're down to around 152 watts. Is the ballast really soaking up 176w or is it actually over driving the T5s?
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Old 12-27-2010, 11:43 PM   #20
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OK, let's start a new thread for the electricity calcs. I made this one a sticky for the RODI calcs.
I will close this thread now.
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