I was out of town for a few days, so my son helped out and fertilized my tank while I was away. Since I have no fish or other animals in the tank there wasn't anything else to do. My lights and CO2 are on automatic timers.
The day before I left, my nano diffuser and drop checker finally arrived from Singapore. I replaced my temporary bamboo diffuser, and a fine mist of CO2 streamed out of the new diffuser. The plants were looking great with the addition of CO2, and I was looking forward to seeing how much the plants would grow while I was away.
When I returned, I was shocked by what I found. A large area of hairgrass in the center of my tank was dead and brown. Large areas of bare substrate were visible. A few clusters of hairgrass along the side were dead or dying as well. I couldn't believe it. I immediately trimmed the hairgrass back in those area to remove all of the dead blades of grass, and I did a 50% water change and dosed some fertilizer.
Here is the tank after the trimming of the dead hairgrass. It looks worse in person, as you can more clearly see the areas of bare substrate.
I don't know what caused the die-off, but I suspect it may be related to low-flow. Before I left town, I did a water change and turned down the flow to minimum on my HOB filter. I forgot to turn it back to full flow, so there was practically no water movement in the tank. When the tank was dosed, it's possible the fertz burned the grass or that simply the lack of movement caused the issue.
I am also experiencing some algae this week, and you can see some of that on the rocks in the image, above.
It's disappointing to lose so much of the hairgrass carpet, but hopefully it will recover quickly and send out new shoots. The other plants seem to be doing very well. The hemianthus glomeratus is loving the CO2, and the tops are twice as big as the bottoms. It will soon be time to trim and replant some of those stems to develop the thick bush effect behind the rocks.