What your describing, as much as its a pain to be without what you want and paid for and expect to be working fine,sometimes things break and we need send back for them to verify its actually broke and see why not working then next step kicks in whether that be....
They say you not using correctly
Fix it and send back working.
Send brand new unit to you .
Tell you it's something you did to break it and it's chargeable to fix or replace .
Or whatever other reasons there could be.
As even though your probably right and it's just simply not working,a big company like red sea would have had umpteen items off all different kinds sent back to them when wasn't even broke or was something customer did to break it so sending out replacements without seeing problem first costs money ( I know you said charge you for another unit so can use and reimburse you if yours is faulty ) but then there left with a faulty unit that is now second hand but been fixed so cant sell as new now if they just charged you for another new one.
I've had some of same frustrations you had with a powerhead ( different manufacturer) which they wanted proof off purchase ( guess to see of still in warranty period) then emails back and forward taking over a week with them just telling me fault finding suggestions on how to possible remedy it which was on instruction booklet that came with it,then asked for me to send back,then they sent out new powerhead which in total took just over a fortnight in total, with all the time me stressing over flow in my tank pffft
I just ordered a dirt cheap powerhead off Internet to make do until was resolved and now got a spare incase happens again.
Even if I can't see where problem is,I often put myself in other persons shoes and try think what could be there reasons and why their policy is what it is ,and the rep even if hasnt dealt with your complaint as you would if liked,maybe she juat following protocol that she has been trained and taught to do by her superiors and on their website, there's probably their returns/warranty procudure explaining what they will do in event something not working or stops working .
Maybe try buy a second hand doser to get and set up and have running for few days to make sure working as you want before you leave town next week. Then if you send your faulty unit into red sea and get fixed then you have a spare.
If not happy with red sea procedures, then you could email relevant department with a suggestion which you think is better,but bare in mind it's a business.
Anyway not meaning to come across as being arsey as do get how frustrated it can be sometimes dealing with faulty merchandise, but they want and got obligation to fix the unit that you know own and I'm sure they don't want to end up with lots off fixed second hand units if just charge you for another.
Hope you get it sorted ASAP and hope all goes well with your tank
