It is time to get the system up to full capacity.  The last component, a half-height 10-gallon tank (yes, that’s really a 5-gallon tank for the mathematically inclined) is now in operation.  Originally designed to be a nursery, it seemed better suited to use as a Bryopsis culturing tank.  I have been pleased with growth rates under the Evergrow S2 hydropnics light, so I picked up another one from Exotic Reef Creations.  So there are now two slug tanks and two algae tanks for the upcoming project.  With the red light from the hydroponics lights and the green from the algae, one might be tempted to think it looks a little like Christmas around here.

Elysia system 12/22/15.

Here’s a better view of the new algae tank, with eggcrate to acts as a substrate and a small Hydor propeller pump to provide current.  Several of the original samples of Bryopsis had started growing in fellow aquarists coral propagation systems, and were provided conveniently mounted on “frag plugs” onto which fragments of coral colonies are normally glued to enable them to grow.  In this case, the growth of the algae on the plugs allowed easy and stable placement in the eggcrate.

Nursery repurposed for Bryopsis culture 12/22/15

There have been a few other improvements as well.  In November, I got the new Neptune Systems Apex controller hooked up.  Although it is capable of much more, it is hooked up to monitor and log energy use, system pH, water temperature, air temperature  (in case of failure of environmental controls in the building), and moisture on the floor.  The unit controls all of the lights, pumps, chiller, and heater, and can, for example shut down the pumps automatically in case of a spill being detected.  Further, the system is completely accessible through a cloud-based interface, which allows control while I am away from the office.

Screen capture of Apex interface 11/16/15

Along with keeping an eye on the system when I am away, the Apex provides a log of some parameters.  For example, when all of the lights were on at the same time of day, pH fluctuated significantly.  The upper plot in the graph show detail of pH rising from 8.1 in the early morning to 8.5 when the lights went out at the end of the day.  Because CO2, which reduces pH through the formation of carbonic acid, is consumed during photosynthesis when the lights are on and builds up at night, it is not surprising that pH steadily rises during the day.

pH fluctuation when all lights are on during day. 11/23/15

Although it did not seem to cause the plants or animals much stress, it seemed worth trying to reduce the fluctuation.  Rather than having all lights on at the same time of day, I set the lights on the algae growth tank to be on during the night.  In this way, photosynthesis would be relatively constant in the system over the course of the day, with the potential benefits of stabilizing pH and keeping consumption of nutrients relatively steady.  I was pleasantly surprised to see the pH fluctuation reduced to between 8.25 and 8.35.  Frankly, the livestock did not seem as excited as I was.

pH when lights in algae tanks alternate with slug tanks. 12/3/15

Finally, I added a small protein skimmer (a.k.a., foam fractionator)  to remove microalgae and organic material from the water column.  Some might argue that suspended material serves as a source of nutrients for the plants, but in my experience desirable algae and plants tend to outcompete nuisance algae when a skimmer is used.  None of the the nutrients provided by the dosing system are removed by skimming, so the skimmer just removes the compounds that are not under my control.  With the height restrictions of the sump, I went with a Reef Octopus BH50, which is designed for small systems.  It has been easy to set up and adjust, and extracts significant amounts of smelly material every day.

Small protein skimmer

For the next few weeks, we’ll be watching algae grow.  After the holidays, it will be time to order up a batch of slugs for the next round of Slug Science!

To possibly belabor a point, the limiting factor in slug husbandry seems to be food.  So more, better food = more, better slugs?

Given how hard most aquarists work to eradicate nuisance algae, including the Bryopsis that Elysia clarki find irresistable, it would seem that growing algae should not be all that horribly challenging, right?  One just needs good, strong light, plus some nutrients to support growth.  The trick is to grow the species one wants, without having the cultures overtaken by undesirables.  In my case, the “good” algae are Penicillus, Bryopsis, and, to a lesser extent, Derbesia, Halimeda, and Avrainvillea.  The primary nuisance I am trying to avoid is “red slime” cyanobacteria, which can overtake and smother the other species.

Plants require nutrients such as carbon, nitrogen, potassium, and phosphorous in significant quantities, along with smaller amounts of calcium, magnesium and sulfur .  Based on my measurements, the desirable algae consumed considerable amounts of nitrate, but adding phosphate did not appear to encourage growth target algae and increased the growth of cyanobacteria.  So, along with calcium (Penicillus and Halimeda use it for structural support) and bicarbonate (a pH buffer and source of carbon) I have been using the dosing system to add potassium nitrate in order to maintain nitrate at about 5-10 ppm.  For everthing else, I have been relying on the artificial seawater mix to provide an adequate balance.   Perhaps not the most systematic approach to feeding the plants.

Broodstock tank 11/16/15

Elysia clarki, enjoying hair algae 11/16/15

It has, however, worked reasonably well. In the photos above, there is a dense growth of Penicillus on the right side of the Broodstock tank, and a mat of Derbesia and Bryopsis on the left.  The resident E. clarki seem quite happy to spend their days grazing without exhausting the supply.  The other tanks are similarly productive.  Nonetheless, it might be possible to increase algae productivity, thereby increasing slug capacity and the frequency of mating and egg laying.

There is, of course, an actual literature on the nutrient requirements of aquatic plants. Some commonly used formulas rely on extraction of nutrients from soil to provide the correct balance of elements.  I might have tried that had I been able to buy the correct brand of English planting soil.  However, based on a number of studies (Kumar et al., 2011 e.g.) Guillard’s f/2 medium (Guillard, 1975) yields excellent growth of macroalgae and does not require purchasing and soaking British soil.

Florida Aqua Farms supplies Guillard’s f/2 medium under the name “Plant Fuel,” providing pre-measured dry ingredients along with a suggested dosing regimen.  Seemed worth a try to find out whether more complete supplementation will translate into faster growth of desirable algae.  What’s the worst that can happen, aside from massive bloom of toxic, undesirable algae?

Mixing Florida Aqua Farms “Plant Fuel” 11/16/15

The components arrived, I mixed them up, and the dosing system is adding 1 ml of f/2 per 2.5 liters of system volume, distributed over the course of each week. We’ll see…

Two days later, the embryos have started to spin in their eggs.  The video below has been filtered somewhat to reduce noise, so they appear to be moving a little more slowly than in the raw data.  Have a look in full screen mode for the complete Elysia-in-motion experience.

Although they will eat a number of algal species, Elysia clarki strongly prefer Bryopsis, which is a feathery filamentous alga considered by most aquarists  to be a pestilent nuisance.  For the past year, I have been benefiting from the struggles of a local reefkeeper who has had a plague of the stuff in his 500 gallon system.  Alas, through rigorous reduction of phosphate levels, his battle  with Bryopsis seems to be coming to an end.

That sent me into a panic.  Well, more like mild anxiety.  Even though it has been possible to maintain my own stock of Bryopsis, it had started to run low.  Hard to believe, but I am having trouble growing enough of a nuisance alga.   In my defense, it is a bit of a trick to grow one form of plague without another taking over.  I was starting to be concerned that the slugs would not be ready to lay eggs if they ran out of their favorite food and had to make do with other algae.

Fortunately (for me), another WAMAS member is in the midst of a battle with Bryopsis.  It required a trip to Virginia, but I returned with a bucket full of soft, feathery algae.  It seems finer than the variety I was getting from the previous source.

Nonetheless,  the slugs are lapping the stuff up.   Despite their reputation for slow movement, slugs are pretty good at moving around when they have appropriate motivation.

Elysia clarki on new batch of Bryopsis, 9/3/15

The adult above dug right in.  As did the juvenile, below.  Up to her rhinophores in Bryopsis.

Young E. clarki feeding on new Bryopsis, 9/3/15

Below is a shot of her cruising around, before having found the food pile.

Young E. clarki, exploring. 9/3/15

Now that they have been fattening up on algae, they have taken on a much deeper green color.  Will have to post some before and after photos next.