Aquatic plants do not rot due to mechanical damage alone. If that were true, every time a pruning is done the plant would rot.
H. zosterfolia is a fast growing plant and fast growth can only be accomplished with fast CO2 uptake, which, this plant is very talented at.
Nevertheless, fast growing plants are a very good indicator of poor nutrition. This is why, for example we often see pin holes and other types of damage on fast growing hygrophila. That also indicates a CO2 shortfall for that plant under those conditions.
Melting, translucency and blackening of any plant is a sure sign of a CO2 deficiency. That should always be the first suspect. Mechanical damage may also be a factor, but mechanical damage does not turn leaves black. Black discoloration is a sign of severe oxidative stress due to the internal formation of lethal doses of superoxides such as Hydrogen Peroxide. These highly toxic chemicals are formed when the plant runs short of CO2. Carbon fixing is halted due to fuel shortage but the light harvesting mechanisms is still running, which causes an overabundance of free electrons from the Electron Transport Chain (ETC).
Just because a plant does well in a non-CO2 injected tank, this observation cannot be extrapolated to dismiss the possibility of CO2 deficiency in a CO2 enriched tank. Time and time again it has been demonstrated that most problems in a CO2 enriched tank are actually due to poor CO2.
It also doesn't matter how well other plants are doing. Just because crypts are doing well in the same tank, that also can never be extrapolated to mean that any other plant should automatically do well. Each species and each specimen must deal with the combination of local conditions combined with their particular ability to uptake nutrients/CO2.
Adding CO2 greatly affects the growth dynamic of each plant individually. Adding CO2 actually makes plants more susceptible to even minor CO2 shortfalls. In a non-enriched CO2 tank the plant is more robust and develops mechanisms to deal with a low supply of CO2 (primarily via the allocation of energy and resources to the production of extra Rubisco, to the production of "high affinity" nutrient uptake proteins and, depending on spectral conditions, to the development of higher density of light harvesting pigments), therefore, low tech tanks should never be compared directly to a enriched tanks.
H. zosterfolia is an obnoxious, invasive weed and is impervious to strong current or to mechanical damage caused by strong current. It's so obnoxious I had to forcibly evict it from my tank. I use MONDO current and I never see this type of damage on this plant...ever.
When you see signs of CO2 shortfalls in your tank do not rationalize it away because there is a likelihood that somewhere down the line, the problem will become more severe and may affect other plants.
Prune the damage away and investigate distribution, flow and/or injection rate. If the specimen is new to the tank then it's also possible that it has to make an adjustment to the tank and will be fine in a short while.
Cheers,
....how to improve CO2 injection just that bit more?.....any ideas?
