PPM - Parts per million

You hear it a lot when people speak about adding plant nutrients or CO₂. What exactly do they mean by ppm? Is ppm a unit of concentration?

Mysterious Liquid Carbon

Few details are given about the exact contents of ‘Liquid carbon’ solutions. Over 45 days, we compared the plant and algae growth in an aquarium receiving liquid carbon against one not receiving any supplement and one aquarium with injected CO2. The plant growth in the tank with liquid carbon was minimal compared to the control tank. Liquid carbon is no replacement for actually injecting CO2 in your tank. It may be able to help starting up a low tech tank but other practices are better at limiting algae growth or cheaper in providing actual CO2.

What gets in the water from slow-release nutrient capsules ? (running)

Some claimed that they are able to grow great plants just by adding these time-released capsules and no water column fertilizers. But if these granules release nutrients into the water column, is there really a case of no water column fertilizers ?...