View Full Version : The big question: can you use tap water to top-off?

05-07-2009, 06:08 AM
I thought I'd ask the question as a few others have, and make a discussion, hopefully with some scientific approach to it.

So, Can you use tap water to top-off a marine, or even reef tank with an algae scrubber?
For me, this is due to a few reasons:
My RO/DI unit isn't very efficient, roughly 5 parts waste water to 1 part pure water
It costs a lot in water bills!
As it gets warmer, and also due to the new fans in the sump to cool the lights for the scrubber, I'm using around 150l a month (40 us gal) in fresh water for top-offs. So 6 times that with the RO unit. It's a waste!

Firstly, I managed to dig up some old test certificates I got from our local water board when we had the shop (still live near by, so identical water), it's a few years old however, but you guys may find it interesting:

Test 1, tap water after leaving the water without using it in the building anywhere over night:

Test 2, tap water after flushing the water out of the tap for 5 minutes:

You'll notice the huge reduction in copper after flushing the tap, we, of course, have copper pipes, not great for corals, but is that level acceptable after flushing?
It was explained to me by the engineer from the water board, that phosphates are actually added to the water to counteract lead, as there were still a few lead pipes in the area apparently (I believe all the water mains in Canterbury are plastic however).
There is a test for chloride there, but not for chloramines, so I presume they don't add them, (I'll double check), so I could probably get away with letting a vat of water settle over night with an air curtain in there.
Nitrates are acceptable at 24-25 ppm, the algae scrubber should pull those out pretty easily.

So the questions:
Is the level of copper (0.03ppm) safe for fish and corals?
Is the level of lead (0.0005ppm) safe for fish and corals?
Is orthophosphate the thing we test for in marine tanks? In our water it's pretty high, at 2.2ppm, but should be taken out by the scrubber again.
Is it worth using a water conditioner? (e.g. Seachem Prime - love the stuff for the ammonia/nitrite/nitrate binding! plus a 5ml capfull does 200l!)
If fluoride is added to the water (I don't believe it is here yet), is it dangerous in the quantities they add to the fish/coral?
Will this help with calcium and alkalinity replenishment?
Let the discussion begin! (and if it is safe, experimentation)

05-07-2009, 06:17 AM
Just found out, orthophostphates are the same thing as phosphates but just expressed differently, maybe it needs to be converted?
Also, for our water in Canterbury, there's no fluoride added and no chrloramines.
Lastly, it's also your right, in the UK, to ask for a water test from your local water board. It's done for free too.

05-07-2009, 11:08 AM
Looks like a job for a test tank with some frags. No filtering needed... just aerate and light, and see if they survive.

05-07-2009, 04:03 PM
I had an idea, but it now seems silly...
I'll say it anyhow, I could run a fresh water algae scrubber on the tap water to make it safe for top-offs, it'd even reduce the nitrate and phosphates, and the algae certainly doesn't seem to be bothered by the weekly rinsing.
The silly part of course, is by saving water, you're going to end up spending money on lighting the fresh water algae scrubber and emitting more CO2

05-07-2009, 05:16 PM
As for copper, remember that algae uses that too.

05-08-2009, 12:36 PM
I think it would be fine if you don't mind running your tank like a crap shoot or are unhealthily excited by games like Russian Roulette. Your tank could thrive then one day have a massive crash. Get it running again - crash.

As we sit trying to duplicate nature's cubic mile of ocean in a tea cup, for success, we need to try our best to prevent large fluctuations in our water chemistry. Public water fluctuates wildly during the year as different sources are tapped and as different chemicals are added as needed to maintain other certain parameters. Our department uses huge doses of copper sulfate to try to kill algae blooms!!

One of our local LFS had a huge spectacular show tank with corals and fish. I could stare into it for an hour. I came in one day and it looked like someone had poisoned everything in it. They had! Plumbers in another part of the building had added some new copper piping. The surge of copper outright killed the invertebrates, and knocked back the ammonia fixing bacteria, which were overwhelmed by the die off.

This same fate awaits those who take in whatever the city happens to be serving up at any particular moment. Haven't you noticed some days when you open the tap you smell chlorine other days you don't? Just one example of the variations present. What happens when three blocks from you house the city breaks a water main and then repairs it? Hard to say.. Too hard!

Topping up your tank with tap water which has various salts in it will result in concentration, the same as when they use evaporation salt flats for salt concentration and harvesting. No, a TS is not going to remove all salts uniformly!

There are much better ways of dealing with your water usage.
We use RO water for all drinking, and cooking, and of course for the aquarium. We use about 4 gallons a day. We use all the reject water! It goes into a five gallon pail that we pour directly into the washing machine. It's the cleanest water the wash ever sees because it has been stripped of a lot of stuff by the RO prefilters. We water livestock with it, we water plants with it, and sometimes we do dishes with it. You could fill the back toilet tank with it though that would be a bit of a scheduling pain. Some people plumb the rejection water out to a 30 gallon garbage can for outdoor use.


Full picture:

Alternative solutions include fixing your rejection rate. 5 to 1 is too much. 4 to 1 is what you should be using. Adjust your restrictor to remedy this and save 20% of waste. If you don't want to be bothered with "handling" the rejection or want it used more conveniently then just use a recycling pump. It pumps the reject right back into your domestic water line. You trade water consumption for a little electricity. My neighbor uses one for just his coffee making RO system which saves him what? two gallons of reject a day?

05-08-2009, 04:46 PM
Some great ideas there kcress, thanks, something to think about!
I had my own idea after you suggested those, I could plumb the output of the reject water into my 5x2x2 fresh water tank, then make an overflow so that it effectively does a water change every time we put the RO unit on for the SW tank. The tank always has really high nitrates with the amount of food our 16" puffer eats. Think the reject should be safe enough? The initial stages (e.g. carbon) remove chlorine from the water to protect the RO membrane from what I remember, right?
Obviously, we only use straight tapwater with seachem prime normally, so the reject, after going through 3 stages before the RO membrane on our system, should be considerably cleaner than the initial tap water (I've got a TDS meter I can check it with)

05-08-2009, 11:40 PM
Yeah! I bet that would work fine.

05-16-2009, 05:51 AM
Where can I get hold of these recycling pumps? (bearing in mind I'm in the UK) Do you have any make/models?
I've just done a test, completely filled a bucket up to 13litres of waste water and got just under a litre of RO clean water out, worked out at 13.3:1 ratio. What's going wrong? That much higher than I'd been told to expect, even by the shop I got it from (http://www.ro-man.com). I don't have a "restrictor" do you mean some kind of valve on the waste water outlet?

05-16-2009, 01:13 PM
Where can I get hold of these recycling pumps? (bearing in mind I'm in the UK) Do you have any make/models?
I've just done a test, completely filled a bucket up to 13litres of waste water and got just under a litre of RO clean water out, worked out at 13.3:1 ratio. What's going wrong? That much higher than I'd been told to expect, even by the shop I got it from (http://www.ro-man.com). I don't have a "restrictor" do you mean some kind of valve on the waste water outlet?

You need a restrictor!!!!!!!!!!

It depends on your system's make.
You want 3 parts reject and one part product. Often the restrictor is something like a tiny plastic hose inside the reject hose or outlet. By trimming the little retrictor hose shorter and shorter you reduce the restriction increasing the rejection. Using two cups you just keep checking and trimming until you get 3:1. I always buy a couple of restrictors because I often cut them too short.

Are you running into an open tank or a pressure tank?

05-16-2009, 02:41 PM
Into an open bucket, however, it's going through around 30ft of tubing to get there, but the flow is still the same even if the clean water outlet cable is only 3ft there's still the same ratio (I've not actually measured, but the flow looks the same).

05-16-2009, 10:29 PM
Yeah it would be the pretty much the same. I was asking because they are substantially less efficient,(but infinitely more useful), with a bladder tank allowing domestic use.

You should get your restrictor correct before anything else.

05-17-2009, 05:05 AM
Well, I've simply put an inline valve on the waste output and adjusted it to slow the waste flow, it is now producing water at least twice as fast now :D
I measured the outputs:
200ml clean water
700ml waste water
so 1:3.5, probably as close as I'm going to get as the valve is very sensitive
380ppm TDS in, 6ppm TDS out. Which gives a 98.4% rejection rate.
This is after 9 months of using the filter fairly heavily and not replacing the pre-filters, so it's probably about time, it was at 1-2ppm TDS to start with. Thanks for the help :D

05-17-2009, 12:04 PM
Great that's a fine solution.

And yes, using a valve is usually really touchy. Glad you got it dialed. And 3.5:1 is just fine.

I usually start changing things when the TDS get's to 10ppm. Everything changed, I get 0 to 1ppm. But my tap water is only about 240ppm. After the carbon block is about 150ppm.

ocean rock
05-25-2009, 02:17 AM
i there i have a veggie patch at the side of the shed were i do all my jobbing " mixing salt , test meters , you now all the things that go with keeping a little bit off reef in a glass box " any way the ro unit is piped up in the shed , and the waste water runs into a water butt " 75 gallon " this i then use on my sweet corn and rhubarb , so no water is wasted ,

05-25-2009, 07:06 AM
We've got a large water butt outside too, but it's completely full from when I moved the 3x2x2 into the 6x2x2 and had to make up 50% of the water, that would have filled the water butt up 3 times over, not really used much of the water in there, after all, we're in a flat and only have a raised patio area + potted plants lol.