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richd 09-19-2013 06:23 PM

My New Tank with Automatic Water Change
OK, so I am starting to design my new tank set up for when I move houses in a month or so. I will be posting pics as I actually build it and will keep this thread updated. I have been doing a lot of research on this subject and have seen a lot of issues with but I think I have managed to engineer a pretty sound solution that should work well. I am looking at a show tank approximately 5'x16"x18" with a sump made from an old tank I already have.

Issues with auto water changer
Fresh water conditioning
So the first issue is how to ensure that the water I am topping up my tank with is good for my fish. We all know that tap water has chlorine and other minerals that need removing. So I looked at using RO with a float valve as auto top off. The problem with RO water is that this pure water is not very stable and is prone to large Ph swings as it has no buffer. I then started looking at the inline chlorine filters that can be found in showers, but I am not convinced that they remove enough chlorine to make the water safe. So I have opted to go for an RO inlet but do small water changes more regularly (5% 3 times a week)

Disposal of old water
The next issue is how I can remove a certain amount of old water. So im going to create two dry chambers in my sump. Chamber 1 will never have water in it but will have bulkhead drain that runs to chamber 2 with a solenoid valve that is attached to a timer. When I want to schedule the drain the timer will apply a voltage to the solenoid which opens the valve and drains the required amount of water into chamber 2.

Chamber 2 will normally be dry until the timer triggers the drain which will begin to fill chamber 2 with water from the sump. I will use a 12v/240v SPDT relay circuit (I will post a schematic once I have drawn it up) and float switch in Chamber 2 so that as soon as chamber 2 begins to fill with water the float switch flips the relay and turns off the return pump to the show tank and tuns on an inline pump that drains chamber 2 to my waste water pipe.

Once the required amount of water has been drained the from the main sump the solenoid valve switches off stopping the flow to chamber 2. Once chamber 2 is empty the float switch returns to its normal position the relay circuit flips back, turns off the waste outlet pump in chamber 2 and turns on the return pump to the show tank.

Risk of flooding when parts fail
The waste water system above seems at first a little over complicated as you could just fit a pump on a timer to remove waste water. The reason for this solution is to prevent the risk of flooding.

The other comment I commonly found was people saying if your float valve fails on your float valve on your fill line the the tank will simply overflow all over the floor as it will continue to fill your sump even though it is full. My solution to this is an unimpeded overflow pipe from the main refugium in the sump to chamber 2. if the sump gets too full then the overflow will begin to fill chamber 2 which will trigger the drain action and start to pump water to the waste outlet.

If the disposal system fails then then Chamber 2 will fill to the top until it is at the same level as the refugium at this point when the solenoid value opens there will be no water flowing as both sides of the valve will be at the same level.

The only way I can have a flood scenario is if both the float on my RO inlet and the disposal system fail simultaneously. I may put a buzzer and/or LED on a float switch in chamber 2 that is triggered if chamber 2 gets full.

The design

I have attached a 2d schematic diagram to illustrate the plan for the sump. I have also done a sketchup model of the sump linked below

My Aquarium Sump design by Rich - 3D Warehouse

I plan to put multiple grade foam in the mechanical filter, then a carbon filter and bio filter in before the refugium.

More info to follow...

Im getting a little excited

Any thought or comments welcomed


Sakura8 09-21-2013 02:25 PM

I have absolutely no experience in DIY and tank engineering so I can't offer any insight or advice. But if you get this up and running, definitely post pics and video! I think this is an awesome idea.

Oh wait. I can comment on one thing: conditioning the water. Some people suggest adding the water conditioner to the tank prior to filling it. In the tank that I fill with a hose from outside, I personally add the conditioner immediately after I finish filling it. The time the fish are in water with chlorine is minimal and if I think they may be in any distress, I add some conditioner halfway through filling.

Tolak 09-21-2013 04:21 PM

Get a cheap carbon block filter, this will remove chlorine & chloramine. You only need cheap because you only need to supply a 1/2 gph drip emitter. Run this to your sump, if you can drill the sump with an overflow & run it to a lower drain you can eliminate chamber 1 & 2. If not toss a float valve on the pump in chamber 2, $12 last time I bought one. You'll change out 12 gallons daily this way, or about 50% every 4 days depending on your sump volume.

The only reason you'd need a larger more expensive carbon block filter is for a higher flow rate, contact time is what removes chlorine & chloramine. At that low of a flow rate you probably wouldn't even need a carbon block filter, chlorine will gas off, nitrifying bacteria that split the chlorine/ammonia bond in chloramine and feast on the ammonia are a problem with municipal water supplies, and can easily be cultivated in your filtration. Many folks doing 29% or less water changes don't bother with water conditioner due to this, with no issues at all.

richd 09-22-2013 02:50 PM

Thanks for the input. Can you hook a drip feed to a float switch? If I use RO filter then I shouldn't need any conditioning? I would jsut be a bit worried about adding any water straight from the tap to my setup.

Tolak 09-22-2013 04:22 PM

Id be more worried about dripping RO with no remineralization then I would with untreated tap. I add 50% straight untreated tap to my tanks due to my water change system, once the overflow is done draining I give it a shot of Prime. They all drain to a sump with a pump & float switch for waste water removal. You'd have to ask the manufacturer of the drip emitter if it could handle the backpressure of a float shutoff.

I do have one tank running that I trickle RO into, 20gpd for a 50% water change on a 40 gallon. I run it through a large fish food container loaded with peat, this drops the pH to right about 5.0, TDS around 25. You will have to worry about pH swings using straight RO, as there are no minerals (hardness) to stabilize pH.

Just for fun I might pick up a drip emitter or 3 & set something up on a 40. Untreated tap isn't that bad if you know what you're working with, and in many ways use it to your advantage.

richd 09-23-2013 04:10 PM

OK cool. I think the top up will be added at a later date. I will add the waste pump first and test water parameters. I do have an idea for a setup to auto dose with conditioner involving a couple of solenoid valves. Im just not sure if I can find any small enough.

Tolak 09-23-2013 06:36 PM

Look for a used IV infusion pump, they're designed to drip a specific amount at a very slow rate.

richd 09-25-2013 07:01 PM

OK so here is the design for my auto doser, to add conditioner during a water change.

It was inspired by Alcohol! I like drinking fruit cider which normally comes in 1 pint glass bottles and is served in a pint glass over ice. Therefore you cant get the whole bottle in the glass in one go. This is problematic if I need to carry the cider bottle, the glass and my wifes white wine back to the table and I dont have a tray...

When this happen I turn the whole cider bottle upside down and place it open end down inside the pint glass. most people panic when I do this because they think that the bottle will empty out and the glass will overflow. In reality as soon as the cider fills the glass and covers the bottle top the cider stops coming out of the bottle because there is no way for air to get in to replace the cider. I can then carry the glass (containing the bottle) in one hand and the wine in the other...

So I have sealed container full of Prime with a drain in the bottom. Attached to the drain is a normally closed Solenoid valve. This then feeds into a t-piece on another piece of tubing that is open at the top and has a second normally close solenoid valve at the bottom. I wire both valves to either side of a SPDP relay which is triggered by a float switch. The float switch sits in the sump at a depth between the full and low minimum water level during a water change. When full SV1 is closed and the main pipe is empty as SV2 will be open. When the water level drops below the float switch the relay closes SV2 and opens SV1. The Main Pipe will fill with prime from the canister until it fills above the inlet. At which point it will stop because there cant be any more air getting in the canister (Bottle in Glass scenario).

The prime will sit in the main pipe until the tank refills and closes the float switch. At which point the relay flicks back to it original state with SV1 closed and SV2 will open depositing the measure of prime into the sump.

The key to this will be the length of pipe between SV2 and the t-piece.

My solicitors need to hurry up and sell my house so I can start building the thing!

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