New Tank, Setup and Dividing

I have a 30 gallon tank divided into 3 and what I found in the summer was that the sections that didn't have filters would get a film on the surface from sitting still for so long. At first I solved this by scooping the film off the surface 2 to 3 times a day. I did find that buying a couple small filters moved the water around enough not to get the film, my fish never got sick or showed ill side affects from the film but it didn't look nice. You should also only need 1 heater but my guys like to hang out by the heater (even though the water stays at 78) so I put a couple of heaters from my smaller tanks that I'm not using anymore into each section. The big heater is set to 76 and I set the other 2 heaters on the lowest setting they have and all of my guys love it!

I would recommend getting more plants and putting them along the dividers, your guys should have plenty of places that they can hide. My guys have sections where they can see each other and flare at each other but they also have plenty of places to hide as well. Also keep in mind with dividers that bettas can jump so make sure the water level is low enough that they can't jump over the divider. You should be able to purchase dividers at your pet store sized to fit your tank or you can make your own using the plastic mesh found at most craft stores.

You could buy a single pump and then use sponge filters in each section. This will circulate the water and the current from a sponge filter is not going to cause stress to your bettas. All you need is a gang-valve and you can run a huge amount of sponge filters off one pump.

The only thing you will have to consider, is how your heater is going to fit. 10L per section really doesn't give you much wriggle room for placement. The Aqua One brand is probably one of the smaller adjustable heaters on the market. A 50 watt should be fine for a 40L tank.

I would read up on fish tank cycling. There are lots of websites that cover this topic in more detail than I will here but this is just a basic rundown. It is your water parameters that will subsequently dictate how often and what percentage of water is changed:

One of the most common causes of death in fish, is New Tank Syndrome. However, it is also one that can be easily prevented.

In a mature system there is bacteria present that processes harmful chemicals into a non-toxic form. Unfortunately, this 'beneficial' bacteria is absent in brand new set-ups. Therefore these chemicals (ammonia and nitrite) quickly build up to toxic levels, and must be manually removed.

This is done through regular water changes. Don't be fooled by anyone who tells you that you will strip out all the good bacteria if you do a large water change. Around 99% of bacteria is adhered to your filter media, and it is quite safe and prudent to perform necessary water changes in the initial stages of cycling.

In general, it takes four weeks to successfully cycle a tank. The rate at which your tank will cycle, is largely dependent on the size of your tank, your stocking levels and your water conditions.

Gravel is mostly for aesthetics so it all comes down to personal preference. Personally, I prefer bare-bottom tanks for anything smaller than 15L. It makes it much easier to clean.

However, if you want to have live plants you will need some form of substrate (unless using a plant with a rhizome), and the substrate can provide a place for some of your beneficial bacteria to colonise.

Unfortunately that air stone offers no media for the beneficial bacteria to colonise. All it's going to do is agitate and oxygenate your water, not cycle your tank.

That is an air pump like I mentioned in my previous post. However, instead of an airstone, you use something like this.

http://www.aquariumproducts.com.au/catalogue_products.php?prodID=2925&catID=29

This not only oxygenates and agitates your water, but also allows the colonisation of beneficial bacteria, which in turn creates a much more stable environment for your bettas.

That looks like the Aqua One brand heater. You would need a 55 watt to heat a 40L tank. 25 watts is not enough and anything over 55 may be too big to fit in your tank.

I would personally upgrade your pump to the next size up. It's always good to overcompensate when it comes to filtration. It is also much cheaper to purchase it online from the store below.

http://www.aquariumsupermarket.com.au/155-aqua-one-sr7500.html

Aqua One is a good brand for the price. I use their air pumps on 6 tanks and have never had any problems with air flow.