The toads should still have access to dry land, preferably with a basking spot. I use a concrete slab standing on top of bricks or other 'legs', forming a table-like structure with the water level a couple of mm below the level of the slab. You could use a turtle dock to similar effect. I find that they prefer fixed islands, rather than floating cork bark etc.
The toads will usually not take food from under the water (although there are exceptions). I generally feed crickets and earthworms, by placing the prey items on the land areas. There will be drowned crickets, but if you add the crickets a few at a time, the toads will take most of them from the land or the surface of the water before they drown. I mainly use black crickets, which aren't so prone to ping about, but rather run and area little more cautious around water. Have some emergent plants or sticks etc can also help as the crickets will climb onto them if they fall in the water.
You can also offer the items from forceps - this works particularly well with earthworms.
Another alternative is to use a shallow dish placed on the land area to contain the crickets. The toads need to be able to see into it and get to the food without the food getting out, though, so you need to find just the right dish!
Whichever way you feed them, make sure that all the toads get food. With a terrestrial tank, there is more space for all the toads to feed, but less dominant ones can miss out when they are fed from a smaller terrestrial platform in an aquatic tank.
It may be more of a pain to feed the toads in the new setup, but you will get a lot more out of them behaviour wise - it is a more natural environment for the spring and summer.
In the autumn and winter you can move them to a terrestrial box and hibernate them at about 7C.
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