As would be expected, plant growth does not appear affected by the diminishment in fish feed. Thats because of the residual nitrate in the system (see Part I).
The exception is with the lettuce heads, which have not grown as quickly. The only explanations I can think of are:
These are different lettuce plants, genetically. I doubt thats the case, but its a possibility. The lettuce starters come from the store and so I have no control or knowledge of whether or when they change seed lots. Still, lettuce seeds are bought or produced by the thousands - no, 100s of thousands by any starter-producer, so I highly doubt I happened to catch the "switchover" to a new batch or breed, and even if that were the case, I doubt one kind of lettuce is going to grow that much more slowly than another.
More likely, the difference has to do with some potassium I added to the system two weeks ago. Potassium or calcium should be added periodically because these are usually lacking in fish feed. Also, the nitrification process lowers the pH, slowly over time. Either potassium or calcium (in potassium hydroxide or calcium hydroxide forms) can be added the raise the pH, and since they are essential for plant growth and missing in fish feed, they are convenient to use because they will not kill the plants or build up over time. As a result of the potassium I added, the pH went from about 6.6 to about 7.2 or 7.4. Thats much more of a swing than I expected or wanted at one time, so Ill add much less next time. By the way, this pH swing was caused by adding a mere 2 tablespoons of KOH to a 4,400 liter system!
But anyway, I am making a big deal out of relatively nothing. The lettuce heads did grow, just not as quickly as past batches. In the meantime, everything else is growing like gangbusters.
Tomato plants that were barely 7 inches tall 3 weeks ago are now 40 inches tall. Their stalks went from sphagetti thin to well over "pencil"-thick. Cucumber plants, in the system 2 weeks, easilly doubled, if not tripled, in size.
You can compare the size of everything in the video below (compared to last weeks video):
click here if video doesnt play
Fish starvation will continue until nitrate levels come down. Hopefully that wont be more than another week or so.
If fish waste solids can be recycled in the system rather thrown out, then the fish feed necessary to grow plants can be reduced, along with costs. Red composting worms play a key role in role in this. I doubt it could be possible otherwise.
Obviously, there are a whole lot of people that have spent a lot more time studying all this than I, but based on limited but real results, I say its worth looking into some more. Ive gotten here by mistake, and I have possibly endangered my fish by subjecting them to high and extended periods of nitrate levels. But the principal appears sound - namely that solid fish waste can be kept in a system that includes gravel-based beds innoculated with red composting worms, where it will be processed by the worms and reduce the amount of fish feed necessary to grow plants. Some balance between the amount of gravel-based beds (worm habitat volume), worm density, fish density, steady feed rates (unlike mine!) and plant growing area must exist. Isnt there an App for that?
Heres another video, this one more about the plants than water chemistry. Also some nice flowers at the end.
click here if video does not play
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