I think I finally determined what caused my dwarf hairgrass die-off several weeks ago. It was a combination of two things. One, I was developing rhizoclonium algae in my DHG as I began injecting pressurized CO2 into the tank. During this time, I was experimenting with the CO2 flow rate, the on/off cycle of the CO2 in correlation to the light cycle, and if that weren't enough, I also adjusted my light cycle during this time. This induced rhizoclonium algae in the DHG, and while I was away, it was not removed and quickly formed a mat over the DHG. The second piece of the puzzle was that I had forgotten to turn the flow of the filter back up to full after cleaning the tank, so for several days, the water flow was very low. I believe that these two conditions combined to simply smother out the dwarf hairgrass.
I have since dialed in my CO2, and my rhizo algae problem is slowly but surely being eliminated. I am leaving my CO2 on for much longer, even with lights out, and this is keeping my CO2 rate very constant. With such a low volume of water in my tank, and with high surface agitation, and with a relatively low plant mass, having the CO2 on nearly all the time is providing much greater consistency than when I was turning it off and on close to the on/off of the light cycle. Since the CO2 level is not rising during the night, there is no threat to the fauna in the tank.
I also have been absolutely overrun with ramshorn snails. Their eggs arrived on some of my plants, and I did not notice them until it was too late. I was removing them several times a day, but finally I decided to just let the population explode and hopefully eat some of the algae in the hairgrass, and then the population should crash. Well, that's the hope, anyway.
The hemianthus glomeratus was trimmed back heavily this week, and after two more trimmings, it should reach the full thickness I intend for behind the rocks. I'll post up a picture of that after it grows back in, and that will likely be the final shot for this journal.
I took this shot before the trim. I have rarely posted pictures of the full tank, since the Petco Bookshelf lacks the minimalist beauty of ADA tanks, but I think it is time to show the tank as it truly appears on top of my bookcase. Please excuse the glare on the tank. I didn't notice it when I took the shot, and I needed the shot in daylight to have enough light in the room to show the full tank without losing the surrounding detail. You may notice the water level is a little low. I keep the tank at this level most of the time to produce higher surface agitation. The design of the included filter produces no surface agitation if the water is any higher, and I found this causes problems with surface scum and the plants suffer.
And here is a closer shot like I have been posting most of the time.
As always, I welcome your comments and suggestions, and many thanks to those who have offered me helpful advice along the way.