I know a vet that had concrette blocks in his tank for at least 10 years and it never had any bad effects on his tank I also know he did religous water changes every week like clock workit was a 500 and he changed about 10% once a week
50 gallons a week. i guees i will always try to go big as far as tanks go. better to have a bigger tank than necessary for many reasons, including less frequent water changes.
