Do you have the Eclipse hex tank? I think so, but can't remember for sure
I looked on the website where you can buy replacement parts, but to buy the acrylic shield,you have to buy the whole hood. You could call and see if they could help out somehow.
I put a root tab about every 6 inches, approximately, among the crypts. I think in my hex, I had 2 tabs. I have 3 in my regular tank. I have C. petchii also now and they are big!
I add 1/4 teaspoon of Seachem Flourish Nitrogen twice a week, and my nitrates are still too low. You know how those test kits can be hard to read, but I think my nitrates are between 0 and 5
ppm. I have to keep working with the nitrogen fertilizer.
I don't know why you don't have algae but that's good! My hex got some sunlight in late afternoon and I had lots of hair algae.
There's no trick to crypts, really, other than the root tabs. I do remember that you had them in the sand before. It's my observation that they grow better in gravel than sand, and I just have regular gravel, not any of the specific plant gravels. The crypts will fill in their area of the tank nicely.