And then this from net pets.
" Automatic water changers are now being installed more and more frequently , and are both simple to set up, and inexpensive to acquire. Check the diagram below for more information :
Notes of importance :
- To install an automatic water changer, you need to be able to drain the excess water that will accumulate. This requires either that it flow into a vat of some sort, to a water drain in the floor, or to a sink (by means of a small pump and hose or pipe).
- Since, more than likely, only a very small amount of water will need to be changed, you will only need a very low output pump. That is the reason a power head type pump can easily be used. Often even the smallest ones will do.
- I recommend using a digital timer. Such timers can be set to trigger at on/off cycles of very short intervals, for example, 1 or 2 or 3 minutes. Mechanical timers usually work only in 15 or 20 minute intervals. Letting the pump run for that long may move more water than you want to, especially if you keep a small tank. Indeed, if you have a 55 gallon tank for example, and you wish to change 1 percent of the water per day, you will want to change only 0.55 gallons, meaning about half a gallon. That is not very much, and only very small pumps, running for a very short amount of time will allow you to do so.
If your pump still moves too much water, notwithstanding the digital timer's setting to its minimum cycle (usually 1 minute), put a C-clamp on the output hose of the pump or power head, and close it gradually more and more, until the right amount of water is moved from the reserve vat to the tank (or sump), in the minimum on/off cycle your timer allows. In fact, anything that restricts the output of the pump, respectively power head, used, will do the job. Small ball valves, shut-off valves, and the like can be used, but be sure that they contain no metal parts, except 316 SS.
- I suggest that you do place an airstone in the reserve vat to keep the water moving around. This will keep it properly mixed and also oxygenated. Water reserve vats must be cleaned from time to time. I suggest at least once a month. This will prevent sediment from accumulating, and possibly breaking down into undesirable compounds.
- Since this is "water-changing" water, it has to be prepared first, and salt added. Preferably use a salt that is low in phosphates, nitrates, and other impurities. Most nationally sold brands are excellent of course. We use Tech-Reef Salt and Hawaiian Marine Mix on an alternating basis, and supplement with Reef-Elements, Vita-Trace, KSM, Iodine Supplement, and the new "Tech-Liquid-Gold" very special nutrient for fish and corals."
