I highly recommend this one. I'm currently using it for my nursery jar. I've used it for my Mars tank as well. It keeps the temperature better than my other heaters.

https://www.amazon.com/dp/B09LM8S7WS?tag=onamzjohnbozi-20&linkCode=ssc&creativeASIN=B09LM8S7WS&asc_item-id=amzn1.ideas.1BLV20P3NQVL8

Edit: I've been testing the temps since I've had it and it's been consistent with keeping the temp regulated and it also has an accurate thermometer. Artemiadaddy recommended it and then he made a video after I had already bought it. My reptile heat matt runs a little hot and the thermometer is 2 degrees off. I just offset the temp for it to be what I want. It works and I'll probably buy a bigger mat once I get my other sea monkey tanks in so they are all on the same pad. I'm not sure how evenly it will heat all the different tanks but that'll make for a nice temperature experiment lol

https://www.amazon.com/dp/B07WC83SQZ?tag=onamzjohnbozi-20&linkCode=ssc&creativeASIN=B07WC83SQZ&asc\_item-id=amzn1.ideas.1BLV20P3NQVL8

I've seen many influencers use this one: https://www.amazon.com/YukiHalu-Submersible-Thermometer-Temperature-Controller/dp/B09LM8S7WS/ref=sr\_1\_1?keywords=yukihalu&qid=1674012143&sr=8-1&th=1