Albert,
The skimmer does more than just remove excess nutrients. It also allows for better gas exchange since the millions of bubbles effectively increase the surface area of the water. Your evaporation rates will depend on a couple of factors:
<ul type="square">[*]Total water flow (gph) as a function of the tank size (i.e. turnover)[*]Relative humidity (keep in mind that an airconditioner which will probably be necessary to control Florida heat lowers the humidity dramatically. In fact, the first air conditioner was invented by this guy named Willis Carrier as a means of controlling humidity)[*]Temperature- which can be affected by your lights as well as ambient temperature.[*]Air movement over or near the water (e.g. fans, ceiling fans, cooling fans, etc.)
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I would suspect on a tank that small anywhere from a gallon every 3 days up to a gallon a day. Keep in mind that in a nano-reef you must watch parameters closely due to the low water volume.
You can rig an autotop off unit, and there are several different approaches:
<ul type="square">[*]Drip type- a fixed drip from a resevoir that is above the tank (or the sump) is used to replace water loss. You estimate the rate of evaporation and set the drip rate accordingly. This type is simple, cheap but harder to set up initially. There are some problems with the drip line clogging especially if you plan on dosing kalkwasser with the top off water.[*]Dosing pump- This is similar to the drip type in that you must estimate the evaporation loss and the program a dosing pump (you can get these for anywhere from $60-200) to "dose" freshwater in the same rate as the evaporation loss. These are often less troublesome than the drip method especially if you are dosing kalkwasser, but is more costly. The other benefit is that since it is a pump, you can put the resevoir anywhere, even under the tank out of site.[*]Vacuum type level sensor- A closed container is placed higher than the tank (or sump) and a bit of tubing is run from the container to the tank (or sump) and the open end of the tubing is placed at the desired water level. When the water level drops due to evaporation, air is sucked into the container which displaces the water which then flows into the tank to raise the water level. These can be problematic, and are not the most maintenance free.[*]Float switch connected to a resevoir- in this scenario a flow switch senses when the water level has dropped and kicks on a pump in a resevoir of fresh water which pumps water to raise the level. This is what I use. It is not the most expensive, but failsafe, and a good compromise between being maintenance free, safe and cost effective. If my float switch sticks, only a limited volume of fresh water will be pumped in (limited by the resevoir) and I simply have to keep the resevoir full.[*]Float valve connected to a resevoir- possibly the simplest solution. A float valve like the one in your toilet allows water to flow gravity-fed from another resevoir which is higher than your tank (or sump). Since the float valve is often large and bulky, most people put it in a sump under the tank where it is not visible.[*]Float-switch connected to RO unit.- This is one of the most maintenance-free options. In this case a float switch actuates a solenoid or a special valve on your RO unit that causes it to kick on when the water level in your tank drops. Since it is connected to your RO unit, you do not have to manually add water to any container or resevoir as is required by the previous options. This option is somewhat costly, and has the added problem that if the float switch sticks then the RO unit will run continuously until you notice and shut it off. What that means is that it can overflow your tank and also that the salinity will continue to drop until you cut the water off. If you don't catch it in time you can kill everything in your tank.[*]Float switch connected to RO unit plumbed through metering device (e.g. LiterMeter) This is the best solution but also the most costly. In this case a float switch actuates a solenoid or a special valve on your RO unit that causes it to kick on when the water level in your tank drops. There is a metering device which only allows a set amount of water to flow in a given day limiting the overflow risk and the salinity risk of the previous option.
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On your nano, if you don't have a sump then you may be limited to the first three options.
I hope this helps.
Ernie
