Part 7 Water Exchange

There are two extremes of accomplishing water exchange. The "bucket brigade" method at one end, and the fully automated exchange method at the other end. I really admire those people that are so dedicated to their fish that they are willing to carry buckets day after day to support their fish. As for me, that's a task that I'm not willing to assume. The other extreme is a fully automated system and there are many different ways of implementing this, some of which can quite elaborate. I have chosen something between the two which I think is quite simple.

Semi-automated Water Exchange System-- Basically, it works like this: once every few days I go down to my basement, turn a few valves, turn on a pump and wait until my "Mix Tank" is full. Then I enable the transfer pump to be controlled by a programmable timer, and that's it until the Mix Tank is near empty a few days later. A programmable timer turns the pump on/off seven times a day, and each on/off cycle transfers 5 gallons to the aquarium. Thus a total of 35 gallons ( 5 gal X 7 times each day = 35 gal/day ) is transferred to the aquarium. A change in programming permits me to change the amount and when the exchanges occur. This system also provides for aging and pre-heating the water, and provisions for using a mix of RO and straight well water.

How Much Water Exchange is Necessary-- The results obtained in Part 1 are dependant on water exchange by some method, automated or manual. I'm presently putting 35 g/d into the tank by a process which closely resembles the drip method. Using the equations for the drip method, 35 g/d results in a net of 30 g/d for a tank of 100 g. The purpose of the water exchange is to reduce the toxic compounds resulting from decomposition occurring within the digestive tract of the fish and to reduce the nitrates to zero. I don't have any way to measure the toxic compounds or for determining an acceptable level. All I can say is that 30% daily seems to result in healthy fish.

RO Collection System--The following picture shows a typical 150gal/day thin film membrane (TFM) RO system. My well water pressure cycles between 40 and 60 psi, thus the requirement for the RO booster pump raising this to 120 psi which is the rated pressure for the TFMs. The RO holding tank has a float valve (same type as a toilet). When the RO tank is filled the float valve turns off and the output water pressure of the TFM begins to rise. A pressure sensitive switch in this line then turns off the RO booster pump.

7-1 RO System with Pressure Booster Pump:
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Transfer Pump and Valves-- I use a single transfer pump and several valves which allows the use of one pump to accomplish several different tasks. On the input side (V6 and V7) are two sources (RO tank or MIX tank). On the output side are four valves (V2, V3, V4, and V5). V2 for the sewer septic system. V3 for the MIX tank or a 5 gal bucket. V4 for the Preheat tank. V5 for the QT tank.

7-2 Transfer Pump and Control Valves:
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Holding Tanks-- Shown on the left is a 125gal RO tank, and on the right is the 155g MIX tank. Both of these are food grade tanks.

7-3 RO and MIX Holding Tanks:
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Preheat Tank-- Water from the transfer pump is regulated by the flow rate valve and is set for 1 gal/min. The water level in this tank is determined by an overflow pipe. Water from the preheat tank is a gravity feed to the show tank located in another room. Water entering the preheat tank is directed to the bottom of the tank while water exiting is taken from the top.

7-4 Preheat Tank:
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Results From This System-- This is a very simple system. I have been using it for over 20 years and never had a leak or a problem of any kind.