You have a high light tank. What's the Co2? Have you tested for Gh? Please do so and post. It looks like a Ca deficiency or an Mg deficiency. Maybe both.
I recently had the same problems with my plants. The L. Repens (which I no longer have) looked exactly the same, but I couldn't figure it out. I had a low Gh. When I started dosing Mg, there was a big difference in their appearance. Their leaves grew bigger and wider.
Although I was getting good results, the leaves of the plants were still growing transparent. Then I added Ca, and the plants took off. They are extremely healthy and many of them are branching out. Right now the Gh is around 14 dh, and their loving it.
Maybe your going through the same problem.