If you already have existing air/water pumps, just buy an inverter. This avoids the AC/DC issue altogether, and lets you use the solar/battery system as a backup to your regular power (for other uses).
I would ck out Ebay. There are all sorts of 12v air pumps out of China. I agree otherwise with Joel and use an inverter from Har Freight which works fantastic btw. Best one I have purchased so far.
I'm using a Shurflow 12V DC bilge pump for supplemental and backup aeration - just pumping water up and shooting it back down onto the surface with a bit of venturi. I don't recommend this - it's just something I'm trying. Thus far, I haven't found a durable bilge pump to use for continuous pumping. I may take my 12V air pump out of my kayak and give it a try.
I've gone the inverter route but my solar system just wouldn't consistently maintain a charge 24/7. You can run much lower wattage with DC and I'm talking about pumping water in this, not air. In the event of a power outage, I intend to run everything from solar with reduced pumping to beds.
I've also tried running everything from batteries/inverter with an automatic battery battery charger attached. Thus far I haven't found a charger which will work reliably - possibly the problem is the constant drain that occurs or maybe the solar charging which also occurs - I don't know. All I know is that when I need the charger to work, it doesn't always do it.
I totally agree with you if you are on solar. Any conversion results in a large loss. On grid not a big deal but off grid every watt matters.
I mostly pump on grid but do run one DC 24/7 from solar/batteries. I tried to go completely off grid but just couldn't make it work with the panels I have. It's still sufficient for backup, which is what I installed it for. If it keeps the fish and bacteria alive until the power comes back on, that will be enough. Two back-to-back hurricanes 7 years or so ago showed me what life is like without power and I'm talking days, not hours.
If a person is preparing for hours without power then a deep cycle or two kept fully charged should be plenty. I like the idea of just running the system full time from batteries/inverter with a charger hooked up. Then, if the power goes off, nothing changes - not until the batteries are dead. Chances are that the power will come back on before the batteries are drained, unless it is due to a major storm. I may get back on the hunt for a charger that works for me.
I would be inclined to buy a little "suitcase" style portable inverter generator; they are practically silent and don't burn very much fuel.
That way you only need enough battery back-up power to last until you can get home and start the generator. If you had 10-12 hours of battery power, you should be covered if you get home from work and find out the power went out during the day... or covered if the power goes out while you're asleep at night.
If you use the generator to also recharge your battery, you can let the generator run out of fuel at night if you want, and run off the battery until you wake up and refuel & restart it.
You could also unhook the generator to use it to run power tools or something if your making storm repairs, and let the system run on the battery... then hook it back up and recharge the battery while the generator powers your system.
I'm looking at the Boyu 12 v pump (http://www.boyu-australia.com/index.php?main_page=product_info&...). Does anyone have experience with this? It is similar to many of the Chinese pumps sold on eBay.
Re: Boyu 12 V
At 18 watts, I'd try it. You could run this full time from a good battery with a 1 amp charger on all the time from grid - or, charge battery from solar.