High on my to-do list when upgrading to pressurized CO2 in our planted aquarium was to try out a carpeting plant. My favorite candidate was Hemianthus Callitrichoides, otherwise referred to as ‘Cuba’ or ‘HC’. I knew of three pitfalls to growing HC Cuba. First, that it is hard to grow. This has proven to be an unfounded fear for our setup (most of the time). HC spreads and grows very quick.
Second, I understood HC Cuba to be a pain to trim and maintain. This is mostly true. Going over three weeks between trims is a no-no, and a HC Cuba haircut results in a lengthy game of net the trimmings. Third, I heard that HC can occasionally ‘lift’ off the substrate and break apart, which is frustrating and is an aquarium aesthetic killer. I was starting to think point three was a myth. . .
As you can infer, I did experience an HC Cuba ‘blowout’. It was a real bummer to experience, but I found that it isn’t the end of the world if this happens. I’ll talk a bit about what causes HC Cuba lift and what to do if it happens to you.
Why Does Hemianthus Callitrichoides Lift Off the Substrate?
When you trim aquarium plants, you may notice that they float to the top of the aquarium. Aquarium plants are buoyant – without being anchored to the substrate by their roots, they naturally will float up.
Hemianthus Callitrichoides will lift off the substrate because of two causes (that usually occur in sequence). The primary cause is that the HC is allowed to grow too thick. Cuba not only spreads horizontally across the substrate, it also spreads upwards in new layers. Regular maintenance of this plant includes occasionally trimming down to reduce the height (thickness).
If trimming is not performed, the increased plant thickness causes increased buoyancy. It is actually pulling upwards with more force.
The increased thickness of HC that is not trimmed than leads to the secondary cause of lift, which is root health deterioration. Plants need light to grow and stay alive. As HC thickens, the lower levels of the plants begin to die off. The Cuba on top has healthy roots, but the HC on the bottom is atrophying and loosing grip on the substrate below.
The result will eventually be that one day you will look in your tank and see a hunk of your beautiful high tech carpet ‘blown out’.
How to Prevent HC Cuba Lift:
It isn’t complicated. The way to prevent HC Cuba lift is to stay on top of trimming. If you don’t let it get too thick, the roots that make contact with the substrate will remain healthy and will maintain their ‘grip’ to hold the planted carpet down.
Beyond that, you do need to maintain overall healthy conditions for your Hemianthus Callitrichoides. This includes providing the necessary fertilizers and adequate CO2 to maintain a reasonably fast growth rate. If the growth rate of HC becomes too slow, even adequate trimming may result in a degeneration of root health and a resulting risk of a blowout.
About the only other suggestion is to setup your tank with a substrate appropriate for HC. This means a substrate that is nutrient rich (to encourage root growth) and that is a good weight to allow the roots to penetrate. I have had no problems growing HC first in Up Aqua Aquasand and now in ADA Amazonia II.
What Do I Do If I have a Cuba ‘Blowout’?
I’ve seen some people try to rectify a Cuba ‘Blowout’ by placing rocks on top of the floating carpet to hold it down. I understand the logic – it takes care of the initial shock and problem of having chunks dangling precariously. However, I can’t recommend doing this. Maybe . . . perhaps, the roots will grow and it will become reattached, but I would put much hope in this method working. One problem is that the rocks will block light and will stunt growth of the only living part of the HC (that which is on top).
In my opinion, there is only one solution: replant. Cut out the affected area of HC. Make sure to cut well into the boundary of what is still attached (if any is left attached) so that the cut edge is at healthy portion of plants that will not lift up.
Then, take the removed section of plant out and put in a Tupperware container. Cut off small sections (around 5 mm by 5 mm at the largest) and replant those in an alternating pattern (similar to this – picture below). Put some space (at least 1 cm) between each plug.
Last, continue good tank husbandry to make sure the new plugs begin to grow back into a full carpet. Having to wait for the carpet to repair itself is tough, but hopefully the experience of a HC blowout will motivate timely trimming in the future.