I had a fluval 305 leak on me starting Friday just before I left for the weekend and noticed it on Monday. It warped the stand significantly and I lost about 5-10gal from the 70. It had a seal that was dirty or something which created a sweat style leak. I learned a few things- always make sure your o ring is clear of debris, always do your tank maintenance the day before you leave and not same day as departure, and never to use a particle board stand again.
do you know what happened with the fx4 that caused the leak? Perhaps your insights could prevent another’s similar experience.