Interesting. I had a closer look at your photo & the instructions on your sticker say 'For 5/8" and/or (hard to see) 3/4" wall thickness do not use this spacer....'. No mention of an 'other' spacer. Have you tried running them on your tank? All the manuals I have, even some older archived ones from 2008 don't show a sticker like yours, so your dry sides are either very ancient or someone's been messing with the stickers?? I'd have another talk with the fellow that sold them to you and also contact EcoTech directly. They're usually very helpful & might be interested in seeing this photo.

Actually Trina from Reef Wholesale has been working with me on it and talking to Ecotech directly for me. Sounds like they're just a really old model and just require the new spacer which she's located for me too. She's been very helpful.