Both high and low calcium levels can cause seizures. The percentage of frogs having calcium deficiencies definitely outweighs the number of overdoses. This is mainly due to lack of supplementation, by us, in captivity.

Brands do matter. One of my retf's starting having tetany last year out of the blue, even though receiving supplements routinely, both weekly Herptivite and every other day calcium/D3. I checked the dates and they were not expired. I switched to repcal calcium with D 3 (as recommended by my vet) and continued to use herptivite and the tetany was gone within 2 days.

So many things can change the amount of supplement they actually get... did the frog eat the night you used the supplement? How many did he eat? How much coated the cricket or insect? How big is the insect(s)? How much did the insect clean off before they were eaten? Did the insect get wet and the supplement washed off? Etc. This is why it is also a good idea to dust their food just prior to feeding. It will help to eliminate a few of these possibilities of less supplement on your frogs insects.

I would consider returning the Reptivite...it is formulated for reptiles. Repashy and Herptivite are great options for frogs.

Yes, it is necessary to also have a separate calcium supplement, one that has vitamin D3 so the calcium can be properly absorbed. Otherwise, it will pass through their intestines with minimal absorption, which can again lead to deficiency.