Monte Carlo vs HC Cuba: same same?

Same-same?

HC refers to Hemianthus callitrichoides 'Cuba', sometimes called Dwarf Baby Tears. MC refers to Micranthemum 'Monte Carlo'.
In the picture above, MC is grown from the top left, while HC is grown from the bottom right. In the area where they meet (the white dotted line) it can be difficult to tell the difference;

Both are common and popular.
And from a distance, they look very similar.
So similar, in fact, that many shops sell them almost interchangeably.
"HC is just a smaller MC"
"Oh, either would be fine"
Nothing could be further from the truth.

Above: MC is a great foreground carpet. From a distance, it is hard to tell the difference between MC and HC.

Similarities

They look very similar.
HC has the smallest oval leaves of the aquatic carpets, about the size of duckweed.
MC is quite a bit larger when grown under robust growth parameters.
At maximum size, MC leaves are about 3 to 4 times larger than HC. However, under lean and overcrowded conditions, MC can be very similar in size to HC.
But this is where the similarity ends.

Night & Day

Above: Monte Carlo is very hardy. It will grow on wood or rock without substrate, and will even grow in tanks without CO2 injection if given enough light and time. The trick to growing them well without substrate is to provide good nutrition in the water. In the picture above, we use APT Complete.

In comparison, HC needs high CO2 levels to grow well and needs soil substrate to grow well. While MC tolerates overcrowding quite well, the bottom layers of HC deteriorate very quickly once overcrowded.

In short, while MC is a really hardy carpet, HC is, by comparison, extremely picky.

The two may look similar, but are miles apart in the care and conditions required to grow them well over time.

 
Of course there are outliers, and the internet is a hotbed of "oh look- I grew HC without CO2" survivorship bias, but the real test is consistency over time, and overall success rate. It is far more helpful to see MC/HC as vastly different than to see them as "the same".

MC and HC Maintenance

Both MC and HC require pruning (in a CO2 injected tank with strong light, every 2 weeks if not 3) to stay in good shape. With MC you can get away with pruning less frequently, while HC requires a much (repeat much) higher level of discipline and regularity.

What happens if we do not prune? The top layers shade the lower layers, which begin to deteriorate, as shown in the picture above. In MC this process is more gradual. With HC it happens much faster. You cannot replace regular pruning with better or more nutrition/fertilization;

As a general rule, prune earlier and earlier rather than later. It is far better to prune aggressively than leniently.

As the bottom layer deteriorates, you need to replant healthy parts of the top layer.