I'd say at about 1000 grams you should switch to something bigger. Some enjoy stretching out and relaxing,in that case I'd switch over sooner. All mine does is hide so I kept him in the 34 qt for longerI think 11" is the biggest size flexwatt. Not sure how large the tubs get, just go up the sizes when needed. I'm paying off a PVC enclosure for my guy so hopefully he won't be in tubs much longer.