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A simple continuous and fail-safe water-change system

David Cottle

Member
Joined
9 Jan 2018
Messages
36
Location
Oakville ON Canada
I set up my planted aquarium in the past year after discovering how much aquaculture has added to the hobby in the 40+ years since I last kept tropical fish. More attention is now paid to water chemistry - of necessity in a planted tank - and I soon wanted continuous water-change, because it just makes sense to me.

I first tried a siphon-drip from the tank combined with conventional auto top-off equipment. I used a float-operated top-up valve and redundant high-level switches with relays operating solenoid valves in the water supply. To be fail-safe, the valves were a normally closed design that had to be energized to stay open in normal operation. I found the solenoids ran too hot, and there was too much hardware in the tank to keep clean. So I went back to the drawing board.

My present design, in use for two months now, has a top-up arrangement that works by siphon, with no moving parts or electricals. I don’t know why this method isn’t in common use - for automatic top-ups at least, if not continuous water change - but I haven’t found it described anywhere. Maybe it is being used and I just haven’t found it?

My setup is shown in the video:

 
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Very good
 
Very nice. Like the thinking of how it behaves in all the failure modes.

I would still be worried about not adding dechlorinator to tap water, especially if chloramine is added.

Standard carbon filters do an acceptable job of removing chlorine but have limited or no effect on chloramine. You need chlorplus filter (is one trade name) in order to remove both chlorine and chloramine.

On another forum one guy wiped out £600 of fish when his continuous water change system dosed all his tanks with chloramine'd water. This was due to the water company injecting chloramine due to a burst pipe in the system. His pre-filter only removed chlorine.
 
Thanks for your comments. Cartridges that remove chloramine are available for this filter. I didn't get one of those because the water treatment plant told me they don't use chloramines for disinfection. But that's not a guarantee that they never will - in an emergency, perhaps. I would probably rest easier if I got the other cartridge.
 
Hi all,
because the water treatment plant told me they don't use chloramines for disinfection. But that's not a guarantee that they never will - in an emergency, perhaps.
That has been the problem in the UK.

Our supply is usually lightly chlorinated (less than 0.5 ppm), but if there is a threat to the integrity of the water main the water companies use emergency chloramine dosing. There was an epidemic of both burst water pipes and fish deaths in early 2010 after some (for us) cold weather.

It is fairly grizzly reading, but have a look at Shane Linder's tale of woe about the Washington DC water supply in, <"Expert, maybe not....">.

cheers Darrel
 
Nice build.. I wonder is it an open top tank? I ask because i have myself a 110 litre open top and it evaporates +/- 1 litre / 24 hours. Than 10 litres p/w would nearly be a top off only replacing what is evaporated.

And reading all this i realize how spoiled i am. My water company asures us, there are no Cl products in our tapwater and never will. Maybe i pay more i don't know but it;s worth that not having to worry. :)
 
Ok i listened again to what you say in the vid.. Language barrier.. :) You explained what is equal to 10 litres per week but you do a 100 litres p/w. :thumbup:
I missed the 100 litre watching it for the first time.

Does this also mean you do not use any filtering? Filtering seems redundant with doing about a complete 100% WC p/w.
 
Btw for your question how to post a vid? It's likely the M dot in the address not recognized by the forum software as a valid video url.

If you look bellow the video in YouTube publicaly after you uploaded it, you see next to the thumbs up and down also a Share button, if you click it a share link pops up, copy that url and put in your repply it always shows without propblems.
 
1 ml/min = 10 L/week (just stating the equivalence)
10 ml/min = 100 L/week
Yes, I still have to filter to remove particulates and also provide circulation through biological media.

Thx for your advice on the video URL. It worked :)
 
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Btw, my purge water siphon tube is located in the outflow from the filter where water should be clearest, and least likely to clog the tubing. Clogging is most likely to occur at the pinch clamp restriction. I look at the purge drip rate regularly, and if it needs adjustment, I periodically open the pinch clamp to flush the tubing before resetting the flow rate.
 
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1 ml/min = 10 L/week (just stating the equivalence)
10 ml/min = 100 L/week

Great system. The only thing I'd mention is that drip system removing 100L a week isn't as efficient as doing a one time 100L water change.

I watched the video but can't remember exactly but I am assuming your tank is 130 litres. :oops:

Your drip system is set to remove 10 ml/min.

Let's round it to 600ml of water being removed every hour. 600ml is 0.6 litres/Hr.
If you are to manually do 0.6 litres water changes every hour, to bring down a pollution of, for example, 40ppm nitrates down to 9ppm, it will take you roughly 313 hours. 313 hours is roughly 13 days of continuous water changes.

If you are to do one 100l water change a week, it will bring the level down to around 9ppm at once.

This result is because when you do smaller water changes, although more often and to the equivalent of one bigger water change, there's a factor of dilution of every 10ml of new water. I am not sure how to explain it but one can calculate it mathematically. So in effect, you're doing one 100l water change every two weeks via the drip system. If you speed it up double that, you'll equal the efficiency of 100l water change a week.
 
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Yes, I realize that continuous and batch water-change volumes aren’t equal. A continuous purge removes a mixture of newer water and older water. I think I’ve seen calculators online for determining the continuous water-change equivalent of a specific weekly water change. But I don’t really care about that. I just care about purging impurities (biowaste, etc.) in the aquarium water at a rate sufficient to keep them below harmful or toxic levels.

For any specific continuous water purge rate, the concentration of each impurity will rise or fall until an equilibrium (a.k.a. “steady-state”) concentration is reached, at which the impurity is being purged at the same rate as it’s being generated. Higher purge rates will result in lower equilibrium impurity concentrations; lower purge rates will result in higher concentrations.

Because I can measure nitrate concentration, I’m using it as my bellweather. For the same daily rate of fertilizer addition as I was using with 40-50% weekly water changes, my nitrate levels tend to be lower now than they were with the weekly changes. So I’m comfortable that my present continuous water-change rate is purging impurities as well or better than my weekly changes. I can, of course, increase the purge rate if I wish. With more experience, I might settle on a different purge rate.

Thanks for your thoughtful comments.
 
I think I’ve seen calculators online for determining the continuous water-change equivalent of a specific weekly water change.

I did mine in excel sheet but sure there are online ones. I just never thought to check, lol.
I don't ever bother measuring nitrates. I prefer a TDS meter and measure conductivity. If it increases gradually, not enough water changes...
 
Hi all,
I prefer a TDS meter and measure conductivity. If it increases gradually, not enough water changes...
That one.
I'm not that advanced yet
It is actually the other way around, you wouldn't know it from most forums, but nitrate (NO3-) is fairly problematic to measure. Have a look at <"Testing strips vs .....">.

Against that conductivity meters have the advantage of giving consistent results over a large range of values, you get a linear response from RO water ~4 microS all the way up to sea-water at 53,000 microS. You really can just dip the meter in a take a reading, you want a low range meter, "Hanna" is a good make.

All TDS meters are really conductivity meters, they jut use a conversion factor (usually 0.64.) to convert conductivity in microS to ppm TDS.

Cheers Darrel
 
nitrate (NO3-) is fairly problematic to measure

I’m using the API Freshwater test. Haven’t found test strips accurate for anything - at least, they don’t agree with API test results. For nitrate, I can’t see the difference between 10 ppm and 20 on the colour chart, so I dilute the sample to get the concentration in the range of 0-10 and factor the result. This changes the concentrations of other components, which may affect results.

Maybe one day when I have nothing better to do, I’ll prepare some standard solutions and check the accuracy of the API test :bookworm:
 
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