I have built an automatic water changer for my 225 gallon African Cichlid tank. Many of the ideas I have used are based on Featherfinfan's design. The main difference being that my water contains chloramines and therefore I cannot filter it out as you can with chlorine. The design is actually very simple and yet effective.
Water OUT / Water IN
Ball valves to each return pump
The first step was to get water into my house under the tank. I already had a PVC water line running along the outside wall behind the tank. I ran this line to do my manual water changes prior to deciding to do an automatic system. The water source is T-ed off of my sprinkler system that supplies from a separate water meter from the rest of my house. I am not charged sewage on this water supply. So, I tapped off of this line and ran it through the wall and under the tank. Once under the tank I installed a ball valve and reduced to ¼" tubing after the valve. This tubing was run directly into one of my return pumps in my sump. I later modified this to have a tee in the tubing and have two water supplies each with its own ball valve. One goes into each return pump to more evenly distribute the incoming water.
Overflow in the sump
Next, I ran another line from the outside to under the tank for my drain line. This line goes to a bulkhead in the side of my sump that I installed for this project. I tried to calculate exactly where my water level needed to be in order to make sure I did not overflow my sump in the event of a power failure. I also had to consider the fact that my sump would drain down to this level while the power was out. Therefore the level could not be too low or my return pumps would loose suction after starting back up. I missed slightly so I installed a nipple with an elbow on the inside of the sump so that I could adjust the level precisely. If you're going to miss, do it on the low side. Installing a nipple with an elbow on the inside of the bulkhead is very easy. If you miss the other way you are out of luck and will have to plug the hole and drill again. My drain line runs out into my yard. I dug a hole at the end of the drain line and filled it with gravel to allow water to soak into the ground rather than making a soggy mess in one spot.
So, I have water in and water out. What about the chloramines? Initially I was dosing my water with the Kent Aquadose. I diluted Prime (Seachem says this is OK to do) to about 1 part Prime and 4 parts water and set the doser as best I could. My goal was to dose for about twice more than the amount of new water being added. The only problem I had was that at this low flow rate the Aquadoser was very inconsistent and I am very impatient. I am sure it would be great for other applications but for this it was just too hard to adjust and I never felt safe about my water quality. After all I am doing this to help the fish not hurt them. So after searching around I came across the Eheim Liquidose. I quickly ordered one online from Petsmart so that if I did not like it I could return it locally. It is designed to dose liquid fertilizer for aquarium plants. But I figured if it doses liquid it doses liquid. Brilliant huh! The Eheim can dose 1 ml from 1 to 8 times a day. Its liquid reservoir holds 80 ml of which 50ml can be used by the device before going below the minimum level mark. Currently I am dosing 5ml of 100% prime a day and changing about 25-30 gallons of water per day. The doser just sits on my hood hanging over the water in the tank. So far I have not had any positive readings for chlorine or chloramines. I also installed an Ammonia Alert by Seachem that will only detect free (read toxic) ammonia. This was done because once the chloramines are broken down by Prime the ammonia part of them is still left in the water. Prime will detoxify this ammonia until it can be processed by the aquarium bio filter but I wanted to make sure that I am adding enough Prime. I was not sure about the Ammonia Alert but I tested it over a bottle of Windex and it gave a reading almost instantaneously. It has not detected any ammonia in the tank water yet.
Screen on water outlet
That about does it. My tank is over stocked and so far it has kept my Nitrates down to ~10ppm. This is the same reading that I kept when I was doing large, manual weekly water changes. It is very early on so I will likely have to adjust the flow rate until I am satisfied that I am changing enough water. At the same time I do not want to be excessive and waste water. I may also have to adjust the dosing of Prime but so far everything looks good. Anyone attempting this please be careful and try to learn as much as possible about your tap water.