Bio Liquid Co2

It still doesn't say what's in it    This isn't really much help

The product contains selected active ingredients that are present in plant metabolism in this or a similar form

Even a solution of glucose (the end point of photosynthesis) would be an active ingredient present in plant metabolism.
I have studied biochemistry at university and although we concentrated on animal biochemistry, I can tell you that metabolic pathways include a lot of biochemicals. My biochem text book is in the attic somewhere - I would go and get it down only my husband is currently painting all the woodwork in the hall/stairs/landing, including the loft access 


It does make one comment further down, though.

There is also a second effect: All organic substances, that is to say those that are carbon based, are bacterially degradable. The filter bacteria feed on them. In the end all that remains is carbon dioxide (CO2) and water.

There are 2 types of tanks - those that contain fish with some plants and those that contain plants with a few fish. It is the latter that needs all the supplements we can throw at them. These tanks are for underwater gardeners and the fish are very much in second place.
The first type is where fish are the main reason for the tank and the plants are just there as scenery. This type rarely needs more than just a bit of fertiliser. All the fish poo and uneaten food is broken down in the substrate. We all know that this makes ammonia, and is one reason that nitrate can get high if the tank is not cleaned enough. But the carbon in all that poo and uneaten food is turned into CO2. A fully stocked tank does not really need added CO2, particularly tanks like mine which have slow growing plants.




None of that helps us with the Dennerle product though.

I've just got back from a trip to Aquarium Gardens. If I had any sense, and if I wasn't so wrapped up in getting more anubias for the axolotl tank, I could have asked if they know what the active ingredients are. 

It also says that it contains potassium, iron, manganese and boron but does it contain other minerals as well? Plants need about 15 minerals but no plant supplement contains all of them. Some contain all but one or two, other's contain a lot less. If this Dennerle product contains only those 4, the other 10 or 11 will still have to be added separately.



Edit:
Just realised that potassium is a macro nutrient, so the Dennerle stuff names only 3 out of 15 micro nutrients.

This is interesting https://www.jbl.de/en/blog/detail/131/the-story-of-liquid-co2-fertilisation-the-co2-content. Haven’t got a clue what it all means though. 

It gets worse if you read the entire set of articles https://www.jbl.de/en/blog/detail/123/the-story-of-liquid-co2-fertilisation?sort_id=1&areas_id=0 specifically the fourth one.

I wonder whether we're getting too obsessed with CO2. I'm fairly sure that the elemental building block that plants require is just carbon. If you think about what a plant is, it is cellulose. Which is a fairly long chain molecule made up of carbon, oxygen and hydrogen. Oxygen and hydrogen come from water, but for most (non-aquatic) plants, the most abundant source of carbon is in CO2. It also has oxygen, so happy days, the whole molecule can be used.

So maybe the liquid carbon supplements aren't so bad if we think about them providing all 3 of the base elements, just in a different configuration?

Obviously I have simplified this to the extent that I have ignored all the other nutrients, macro and micro, that plants need to make more complex cellulose based molecules.

You would require a drop checker in order to check the CO2 level in the tank.
I use a fire extinguisher as my CO2 source. They are a lot cheaper to buy initially and to refill.
It might be worth considering a regulator with gauges in order to check the working pressure and the gas remaining in the cylinder.

I must admit I didn’t need a drop checker when I had the Seneye in the tank. I just used the pH drop to gauge the amount of CO2 that I was injecting from a table of values based on kH and pH.
I currently use a drop checker as I find it a simple way of getting the CO2 level right as I tend to tweak my levels up gradually (in case of an overdose).

Thanks @daveyng

Keep us informed!

Have the Carbo Elixier Bio and started dosing using 5ml per day. Recommended dosing is 1-3 ml per 100 litres. My tank is heavily planted so this works out about 2/3 of the maximum dose for my 270 litre tank.
I have taken a couple of pictures of the aquarium at this stage so that I can make a comparison on probably a weekly basis (depending on growth rate).
States on the packaging that it is not a complete fertiliser and that it dangerous to exceed the recommended dosing levels.
I’ll keep you posted as time progresses and will include pics on my next update.