Although the slug system does not require much in the way of chemical supplementation, the plants do require a little input beyond the weekly replacement of about 25% of the artificial seawater in the system. Because there are no fish or other creatures generating nitrogenous waste for the plants, I am adding small amounts of potassium nitrate (KNO3). Plants also require phosphate as a major nutrient, but they consume it in much smaller quantities, and the presence of some cyanobacteria (blue-green algae) implies that there is at least a small amount. I am also monitoring calcium (Ca2+), which is used by some (e.g., Penicillus and Halimeda) but not all (e.g., Bryopsis) of the food plants. Possibly most important is bicarbonate (HCO3–), which acts as both a buffer for the system’s pH and as a carbon source for the growth of the macroalgae. For the moment, the goal is to maintain ~5 ppm NO3–, ~400 ppm Ca2+, and ~3.2 mEq/L HCO3–.
Up to now, I have been adding supplements as needed to maintain parameters, and it has been fine. However, being away from the office due to other obligations or short vacations can cause parameters to fluctuate. This can lead to slowing of the growth of food plants, enhanced growth of pest algae (defined as species the slugs won’t eat), or both. Plus, it might be nice to take an extended vacation.
In an effort to stabilize parameters, I have added a Bubble Magus BM-T11 three-channel dosing pump. It can add NO3–, Ca2+ and HCO3– independently, in whatever volumes and intervals I choose. As part of the kit, I also got a set of reservoirs, a small fitting to mount the tubing on the sump, and a set of three reservoirs to hold solutions. Always fun to open the box and set things up.
Then it was time to assemble things, fill up the reservoir, and see how things go. The pump was remarkably easy to program, but each of the the reservoirs had a poorly sealed connection on one of the critical fittings. All it took was a little cleaning and silicone sealer, and we were good to go.
Now it’s time to put the feet on the desk, chomp a cigar, and let the pump do all the work. Now that the pump is adding supplements at a known and constant rate, it should be straightforward to adjust the doses up or down to optimize plant growth and slug health.