I was just reading that algae problems can be caused by a low CO2. I have a 265 litre tank with lots of amazons in it and only four angel fish. I must say that since I have been doing partial changes with Woolworths bottled water (0 PH and no amonia) I have only been doing a 10% change every 2 weeks. I am, however, getting a bit of algae on the leaves of the plants as well as a bit on the glass (( was getting this before the less frequent changes). I do understand that doing more frequent water changes should help. However, I have also bought what is labelled on the box a 'CO2' diffuser. It did not have a package insert but the guy at the pet shop explained that you put the one black box in the tank (it has a sliver plate in it) then plug it in and then turn the knob on the other black box outside the tank (goes from 1-10) to regulate how much CO2 must go in. I have been using it set at 4 and lots of minute bubles ooze from it into the water. It does not seem to have had any impact on the plants. They are not doing too badly at all though, surviving but not growing fast. However, I was reading one of the forums where someone said you need to have a tubing and yeast and sugar as well as the CO2 diffuser. I would be very grateful if someone could advise me. Thanks.

I'm having a lot of trouble visualizing this contraption...
I'm only familiar with DIY setups and similar...
the general idea is:

A sealed canister (could be a soda bottle, I have the nutrafin CO2 canister) with a hole on top for an airline to be attatched has mixed room-temp water, sugar, and yeast inside it. As the yeast consumes the sugar it releases CO2 which causes pressure in the canister and the CO2 to pass through the airline into the diffuser in the fishtank...

what you're describing sounds like a pressurized system...but the diffuser is really hard to picture. any way you can get a name of the diffuser or who its made by? is there a large gas canister with CO2 in it that you had to buy...?

Thank you, I have no idea. It just has a sliver plate inside the black box that goes into the tank. I struggled to get the Tetra or Sera one, no shops stock any CO2 systems except for one where you have to buy a huge cylinder etc etc. and the cost of all of that was nearly the same as my tank. I asked some shops to order a tetra or sera basic one for me, but although they said they would, they did not do so, so I finally found a shop that had this device in it. I think they like the plants to die so you keep coming back to buy more.