I made the same mistake. I went from keeping discus and exotic plecos to Tanganyikans but kept up my water change routine. I kept losing some each water change until the importer I was get tangs from told me to do smaller water changes for them. I lost way more than $10 during that lesson lolThat might be the answer right there. It was a good 60-70%. I've always kept Central and South American and just recently started with Tanganyikans and Victorians.