Hi we have a black moor who is about 7 years old and hardly moving just sitting at the bottom of its tank we change its water every 2 weeks and feed him once a week any advice please

No results on water sorry but changed his water on Friday and put some but put some interpet anti internal bacteria stuff in and not made any difference

Presumably you mean you feed him once per day, rather than only once per week? [If only once per week, likely long-term malnourishment is to blame.]

You haven't provided much detail for us to help you with (eg tank size, quantity of water changes, type of food, water test results, photo, etc) but, in the interim, 25% water changes several times per week are likely the best option to see if he perks up (and better than medicating him).