Recc's on building a dosing container

[Steve1500]

I am building a dosing container for my 75G DT/30G sump and I will be using a GHL (4 pump) doser. I have limited space for the dosing container and am debating on a 3 vs 4 chamber setup. If I go with the 4 chamber setup then each section will hold ~1.2L. If I go with 3 chambers, each section will hold ~1.6L. One concern is that ~1.2L is not a lot of fluid and I might be topping off all the time. I understand much depends on my water parameters also. I don't have any SPS in the DT yet, but I will add in a month or so.

I will obviously auto dose for alk and CA but Mg and the trace elements are up for grabs. Here are my current options:
3 chambers (1.6L each):
Dose Alk, Ca and Mg
Dose alk Ca and some thing else besides Mg (I can dose this by hand as needed)

4 chamber (1.2L each):
Dose Alk, Ca, Mg and something else

Thoughts on 3 vs 4? Also, whether I dose Mg or not, what trace element would you recc I dose (what typically requires frequent dosing)?

 

[Reef of Fillory]

There's 1,000 ml in 1 liter, and ~3.7 liters in a Gallon

Even if you had to dose 100ml/day of whatever is in your containers, you'd get 9-10 days per 4 chamber container before needing to refill from a gallon jug [for example]

If you think that you might try Triton at some point, 4 containers would be a plus

Auto dosing Magnesium is nice, but imo not necessary - test for it weekly or bi-weekly and adjust accordingly

If you're planning to stick to a water change routine, you're unlikely to need to dose trace elements, if you plan to get lazy on water changes (like me) then there are a number of trace element programs out there which suggest daily/weekly hand dosing routines