My tap water has a very low TDS (79). All my other parameters say that I should be able to breed in straight tap, but I can't. I'm taking my TDS down to 20ish with RO. Now I'm having success. My best advice is to add more and more RO to the mix until the fish succeed. Buy a TDS meter. That will help you know when you reach the sweet spot. BTW, I'm very lucky. Once my eggs hatch into wigglers I can switch to pure RO waste to raise them until adulthood, so no waste! I get to use all my water. Now that is a blessing.