WaterNotes

20: Four months

Its so hard to believe that this tank is at four months old already! The stargrass has taken off in the last week or so, while the shoal grass and the turtle grass still look as though they are refusing to grow much at all. Ehh. The first tank was like this too though, the Halophila went crazy while the larger grasses took their sweet time in acclimating to tank life as well as throwing out new plants and such. Plus, they had more light in the previous tank, which I imagine helped growth quite a bit.

When I last wrote I was in the throes of a now-and-then cyanobacterial bloom. It would arrive for a few days, die back and the tank would look great. Then it would be back. Perplexing at the least. Falling nitrate levels are thought to be a trigger for cyano blooms so I was careful with the dosing regime. It was then I realized that my tank was sucking down about 2.5ppm NO3 in less than 24 hours between doses. Considering the volume of the tank that’s about 130mg of NO3-. Quite a lot.

Likewise, the phosphate levels will fall daily from 0.15ppm as best can be read, to relatively zero levels. The tests come up clear and I even used a Salifert kit for this nutrient. So, again, considering tank volume, that’s roughly 8mg of phosphate each day. These plants must be growing some serious root systems! The nutrient ratio for this tank is then about 130N:8P or.. 16.3:1. (And for more on that infamous ratio see here.)

Now, for those that have been paying attention to these logs, the new numbers tell another interesting story. Inside of a month we went from roughly 2.7mg PO4 each day to 8mg each day. Nitrate made the same 3-fold jump from 40mg to 130mg daily. That is a lot of turnover! And the tank doesnt even really look like a jungle yet. Hmmm.. I may be in for it when this tank reaches the stage of plant growth I’ve been aiming for.. will I be up to hourly dosing at that time? I certainly hope not!

**Note: You may have seen higher numbers quoted when this was first posted. Apparently along with my issues in gauging volumes on sh.org I also have problems with my math! Blame it on my lovely handwriting.. I had notes that it 5ppm per day and not over the actual 48 hour period. So, numbers have been adjusted. A three fold jump is also a lot easier for me to believe.**

The question after all this math was to decide whether to dose daily, dose weekly, or do some variation in between the two for a regime of adding in nutrients. Considering the amount of nitrate and phosphate I need to add, and the knowledge that too much phosphate at once chokes the system with diatoms and green algaes, I went with every other day dosing. So, now I add in 5ppm worth of NO3 and 0.3ppm worth of phosphate every other day when the lights kick on. Workin’ alright so far, no unnecessary blooms.

After fooling with the dosing regime to better match the uptake rates of all these hungry plants I discovered, with a little more testing, that my alkalinity levels were falling weekly. From acceptable ranges after the water changes of about 4 meq/L (a measly 2gals) on the weekends to dangerously low levels of 0.5 meq/L by Friday afternoon. Just as before, the plants are attacking the alkalinity carbonate levels of the tank scavanging for carbon to use in growth. They’re consuming about 0.6 meq worth per day. Not sure what that is in dry weight. I’ve seen it before in the tanks with seagrass, but I guess I must have forgotten this important lesson. So, to all those starting planted tanks, beware not only the N and P, but also pay some thought towards the C! I think after another month or so I will start CO2 supplementation on this tank. That should allow for significant growth in the mean time from the plants.

Getting back to the problem: There are two ways to deal with this, and I’ve taken the ‘fraidy-cat way out for now. You can supplement back alkalinity via sodium bicarbonate (or baking soda) dosing during the week to stabilize KH. Or, you can pump CO2 into the tank and hope that the plants convert from carbonate stripping to use free CO2 in the water for their carbon needs. Carbon supplementation in marine tanks isnt a well formed concept so far. I’m not even sure it should be attempted by anyone keeping corals of any sort as it will mess with their own growth patterns. I also dont know how it will affect fish physiology if we run into acid water situations. So, for now, its a big elephant I’ll leave in the room when I have more time and energy for such things.

You may notice I added in some rock (dead rock to be exact..) and various macroalgae - prolifera, suction cup and C. peltata. They have taken off running. I can already see how prolifera got its name. I am concerned they will outcompete the grasses too much, but, I was hoping to integrate them into an eventual artistic design in the tank.

So far the ‘design’ part of this project has barely even entered my mind. You can see that the stargass has invaded spaces in the turtlegrass bed and that the shoal grass and manatee grass are just hanging on by threads. The Caulerpa macro’s I added are also a little weak, but they just went in three days ago. There is Halimeda on the rock formation to the right that hasnt done a thing in nearly a month, even with good calcium and alk levels. Its just taking its sweet time to come all together. But then, everything is a process in life, and at least this one has been a joy to watch unfold so far. Hopefully by the next monthly installment things will have picked up with the blade grasses and the stargrass will be back to neon green standards and growing into a thick carpet at the front.

If you’re keeping score the species list goes somewhat like this:
Halophila engelmanni
Thalassia testudinum
Halodule beaudettei
Syringodium filiforme
Halophila decipiens (hanging on just barely with two little leaf sets)
Hippocampus zosterae
Palaemonetes vulgaris
Caulerpa prolifera & peltata
Assorted snails, wormies and copepods..

You may remember I had suffered over the revelation that I had brought back the threatened status seagrass, Halophila johnsonni, on my last visit. Its a very fragile grass. And its really really small. As far as the Halophila’s go, stargrass is the biggest, then paddle, then Johnson’s. The whole plant is perhaps the height of your thumbnail. I had a small little rhizome with a few horrid lookin leafs. What to do?

In comes my quasi-brilliant idea for the seagrass ICU, which failed terribly with this species, but might be good for later use. Grab a ten gallon tank, slap a 96watt 6700K PC over it, fill with saltwater, stick in a powerhead and you’re good to go. Be sure you have lots of nutrients in there too. Now, I added in Caulerpa’s to keep the nutrients in control to discourage pest algaes and then went in this elaborate ‘grass setup. I took small plastic plant pots and filled them 3/4 with potting soil then some carbon, then aragonite sand. I also put in some broken up Seachem Fluorish tabs to be safe. Then in went the seagrass rhizomes and the waiting began. Johnson’s seagrass never even picked up a single shade of green. It languished and mocked me and sent me evil looks and eventually died entirely about a week ago. Sigh. But, it was a good attempt at least, and I think this system would work well for ‘babying’ other new transplants. I hope that someday I can figure out good methods for seagrass transplants, not just for us as hobbyists, but for the ‘grass community too.

The last thought for today is this: I wish we had access to more seagrass species. While I think I am dangerously close to the Noah’s Ark syndrome in this particular tank I’m eager to learn and grow other types of marine angiosperms. If only we didnt have customs officers!

Yummy cyano invasion before bumping alk: