"I have a 10 yr old hot water tank. It burns a fuse about one a week , change the fuse and it works fine for a few days or so. There is always plenty of hot water, never run out. I tested the elements and they are fine. I have not tested the thermostats. Not sure how to. What might cause this tank to burn fuses on just an occasionally each week or two but work fine?

Fuses?

You might have a wiring problem rather than a water tank problem.

If you're sure it's not a wiring problem, then there are a couple of water tank problems that could cause what you describe... but on a 10-year old tank, I'd recommend replacing the tank rather than replacing parts.

The thermostat could be going bad - or you could have a torqued element that is very near the side of the tank... and when it gets hot it's moving a hair and touching the side.

Yes it does have fuses.

Wire looks fine between fuse box and tank. Only 10 feet away and wire is visible. It is my rental. The tenant told me he saw a spark inside the box when he would change fuse and turn power back on. I did this only spark I saw was normal. I did tighten things up though. Elements checked fine yesterday. Did not know how to check thermostats.
Thanks and comment if you have any further info.

I'll move this over to electrical in the hopes that our Electrical Expert might have a tip on testing the thermostat.