We have a reasonable sized fish tank in our lounge, and we have never really managed to keep plants alive in it. But, I have just found out that the reason is a lack of Carbon Dioxide in the water – obvious with hindsight!
You can buy, at fairly steep cost, CO2 injectors – not much change from £100 is pretty typical (and it can be more). Some folks have had good success with yeast based supplies, so my first trial, largely to see if it made a difference, was to knock up my own using a 1 litre fizzy drink bottle, some baking yeast, sugar and water. A foul looking brew, but it worked fairly well :-
But, it was a palaver to keep it running well, and it didn’t have enough pressure to be able to get through a diffuser I bought from e-bay for about £8. So, I thought that since CO2 is used for home welders, there must be a way of using a home welding supply rather than just shelling out for something that was basically the same, but badged as for fish tanks (and 10 times the price). The gas bottle and regulator were easy, from Machine-Mart :-
The challenge was to connect the small bore gas pipe that fits the regulator into the larger bore pipe for the tank. I tried all sorts of things before spotting the obvious – the small bore pipe would fit inside the larger pipe, with a bit of force … and make a gas-tight fit. A couple of cable ties to keep it all in one place when pressured, and it was there!
The end result was a very easily controllable flow of CO2, with a total spend of £20 + Gas. The first bottle (cost £12) just ran out, after about a month or so – so not super-cheap to keep supplied. But, the plants are doing superbly.