Water Chemistry and Tank Size.

[scunfcu]

Debating to setup 90G or 40G SPS/LPs tank. Does a 90 gallon tank holds more Calcium, alkalinity and Magnesium than 40G due to water volume? In other words it would take twice as long for the SPS/LPS corals would have consume Calcium, alkalinity and Magnesium on the 90 gallon compared to 40 gallon?

If I can get away without having to perform two part dosing on the 90 gallon and just perform weekly or bimonthly 20% water changes.

 

[Sk8r]

Not proportionately, but bigger is more stable. But if you can set up a kalk ato, ie, by putting lime into the ato reservoir, you can automate the whole cal, alk, mg thing without even needing a controller. Evaporation drives the ato to deliver the limewater, and bingo, you're dosed.
OTOH, there is a complication. That kind of dosing works well for a packed (wall to wall stony coral) 50-70 gallon reef, but a 90 if thick with coral could require a calcium reactor to keep them fed.

 

[gone fishin]

IMO the consumption will depend largely on the growth, amount and type of corals plus a few other factors such as coralline growth.

A very simplistic answer is yes more volume will equal more alk, calc than in a smaller volume, assuming same conditions. I would suspect in an SPS, LPS dominant tank at some point dosing of some sort would be required. If this is something you do not want to do then maybe rethinking your stock goals are in order.

 

[gtareef]

The short answer to your question is depends.

Just think of CAL and ALK are food. Corals will consume CAL, ALK, MAG if they are healthy and growing. The more corals you have the more food you would need to keep them happy. If you are relying only on water changes without dosing then you are limited to how many pieces you can keep without starving them.

If I were you, I would test weekly for CAL, ALK and MAG to make sure water changes are enough to maintain proper parameters. If levels are dropping too quickly then you will need to dose.

I hope this helps.

 

[scunfcu]

Thanks, in that case I may just settle on 40G for growing SPS/LPS frags. The 90G would require more resources to maintain.