Originally Posted by MoneyMitch
safe to say when kh starts to drop that your tank is "full" as far as balance goes? then when its stable their is more room for plants since the plants will use the ammonia/ammonium before they start to use the cao3 in the kh? cao3 i think is what its called that the plants convert. since it takes less energy for the plants to use the ammonia/ammonium then the cao3
Not quite. The ammonia is a source of nitrogen so ammonium, ammonia, nitrite, nitrate... That's the nitrogen order of consumption for plants from easiest to hardest.
The carbon source is primarily CO2, the easiest. Without getting all chemical, the carbon component of the KH constituents, CaCO3 is one but there are other ions involved, becomes the next best source.
KH drops when the plants are using more carbon than the fish are producing with their respiration, CO2. The assumption is that there is enough ammonia being produced to let the plants have enough energy through photosynthesis to pull the harder carbon sources in. There also needs to be enough of the other nutrients and light for this to continue or there will be imbalance. The KH drop indicates that imbalance is pending as, if left alone, carbon becomes scarce and the plants stop taking in ammonia which leads to more nitrite and nitrate due to the nitrifying organisms (NOs for short) picking up the slack with the ammonia consumption.
No big deal, tank stays balanced, water changes look after the higher nitrate production, NOs increase in numbers but the plants may slow down and I suppose this is where algae and other stuff may appear. So either adding more fish, injecting CO2 or increasing KH will serve to rebalance the whole equation more to our liking. Each has its drawback. I like the idea of adding KH if the fish load is already where I might want it.
As mentioned, some plants may not do this, I haven't looked into which do and don't. A good mix of plants might ensure that there are some that do. I think that some just don't do it well but when push comes to shove, carbon is carbon. True soft water plants might have more problems. I happen to have water that is 23dGH so I didn't pick soft water plantsat least not intentionally. That may affect my results.