I have Ingo's book. It is decent. The fish on the cover is not a zebra pleco, it is an L236. The book has a lot of info on foods various plecos eat.
I have been fortunate to meet Ingo and chat with him a bit re plecos. The funny part of this is over several years I have attended events where he was either a speaker or attendee. I wanted him to autograph his book for me and I kept forgetting to bring it. The last time I saw Ingo was at the 2016 CatCon in VA. When I ran into him in the hotel lobby I mentioned that once again I had forgeotten to bring the book. He replied, "What a shame, I came all the way from Europe just so I could sign it for you,"
I also have a book I got as a gift. It is unique in that it is written in both German and English on the same or facing pages. it is well iluustrated.
Loricariids of the Middle Rio Xingu. It is authored by some of the biggest names in the pleco world: Mauricio Camargo, Heriberto Gimênes Jr., Leandro Melo de Sousa & Lucia Rapp Py-Daniel.
I think the above may be out of print. It is a much in demand book apparently and hard to find. Some of the picture in it are supplies by Ingo. There is a big section for zebras, pgs 163 - 170. Many fish get only 2 pages. It is illustrtaed and the pics alone are worth the price of the book, imo.