In the next month or two, Im planning to set up a 400 litre tank dimensions are 5ftx2ftx2ft it will be general community stock, nothing massive or too messy
I am limited in experience with external filters, so my questions are?
1) How many litres/per/hour should I be after filters wise?
This depends on your goals, but for the stated general community our starting recommendation around here is 5x turnover, which would be 2000 liters per hour. People who go for planted tanks sometimes go for 10x turnover or use extra powerheads to increase movement in the lower portions of the tank. You want to dig up the actual flow rates from the manufacturer specs, not any "recommended tank size" type numbers. And its good to be aware that they will have pushed their numbers as far as possible and your flow in truth may actually be a bit less, so raising your flow rate somewhat beyond your goal may actually reach it better.
2) I have seen the fx5 filter, but am i better off with two smaller externals so i have a back up incase one breaks?
In my opinion, yes, you are better off going with two lesser sized but good external cannisters on a big tank. You are completely correct that the "backup" feature is very valuable, also you can alternate cleanings. The other nice thing is that pump noise is not linear and shoots up quite a bit more when you go to the biggest machines. You are paying a bit more probably to split the work in two, but its worth it. In fact, if you can afford it, you might look at the 3 or so choices of big machines that eheim offers. Its top dollar of course for these top machines but they are pretty awesome.
3) What is a spraybar and what are the benefits of using one?
Just a long ending tube with holes drilled so you can suction-attach it along the water surface and it will maximize the surface disturbance or is quite customizable depending on the amount of surface disturbance you want (surface disturbance being a trade-off of course between oxygen gained and co2 lost.)
~~waterdrop~~
