Yes, you can combine the both Nitrate and phosphate powders in the same volume of water. The numbers look fine for 3 doses per week. Just dose 10 ml at a time. make the numbers easy.
As far as traces, just assume 6g per teaspoon and call it good. There is no need for accuracy at all.
Just rinse your dropchecker with distilled water if you have it. If not just use a bit of the 4dkh water. Worst case just use tap water and you'll be fine. In general, avoid acidic or alkaline cleaning products for obvious reasons.
Cheers,
As far as traces, just assume 6g per teaspoon and call it good. There is no need for accuracy at all.
Just rinse your dropchecker with distilled water if you have it. If not just use a bit of the 4dkh water. Worst case just use tap water and you'll be fine. In general, avoid acidic or alkaline cleaning products for obvious reasons.
Cheers,