Help!! Low pH

Actual water volume would probably be more like this:

65 less glass (they measure on the outer dims, not the actual inside volume) = 55g
55g less rock (maybe 5g displacement or more) = 50g
Sump = 29g but at operating level it's likely more like 15 or so

50 + 15 = 65g

Salt content is a simple linear equation so if you have 65g @ 35ppt, 65x35 = 2275 (not a relevant number just a reference figure, I would just call this "total salt), if you were to take out 2 gallons of water in one shot then you would do 63x35 = 2205 (this is your new "total salt") and now add 2g RODI so you take 2205/65 (your new water volume with the second "total salt") and you get 33.92ppt. So the answer mathematically is there is no way that you dropped your salinity by 2.5 just by removing 2 gallons - even less chance that this happened incrementally over 2 days, because that would drop it less.

For you to drop 65g from 35 to 32.5 gotta do the math backwards now...you would have to replace 4.65 gallons of 35ppt water with RODI in one shot.

Now if you are using a standard refractometer, you have a margin of error. Luckily I have a Milwaukee meter too...

 

Hmmm...now that is better data - I would say if you take a starting point of more like 34.5 and a drop to 33

So here is the equation that you would use to solve for volume given that data

(x-2) * 34.5 = x * 33

Or more generally

(system_volume - (removed_volume)) * starting_salinity = system_volume * ending_salinity

solving for system_volume x = 2 / (1 - (33/34.5)) = 46. That doesn't sound right, unless you have a ton of rock and very little in the sump when operating...

 

To get that equation to work out to x=65, your removed_volume would have to be 2.8 gallons, does that sound more accurate?

PS

<< nerd

 

It would really have to be more than that actually, because if you take that equation and then break it down daily with the starting ppt and ending ppt and 65g for the system volume and solve for removed_volume, then add all those up, you'll end up with a bigger number. I think.

 

RV = SV - ((SV*ES)/SS)

For 8/10 SS = 34.5, ES = 34.333

8/11 ES = 34.166
8/12 ES = 34
etc

It looks like on avg it's dropping 0.5ppt every 3 days, so 0.167/day

RV 8/10-11 = 65 - ((65*34.333)/34.5) = .314g
RV 8/11-12 = 65 - ((65*34.166)/34.333) = .316g
RV 8/12-13 = 65 - ((65*34)/34.166) = .315g

So for those 3 days, 0.945g x 3 = 2.835 over 3 days, but that daily number is just going to keep increasing

RV 8/13-14 = 65 - ((65*33.833)/34) = .319
RV 8/14-15 = 65 - ((65*33.666)/33.833) = .321
RV 8/15-16 = 65 - ((65*33.5)/33.666) = .321

next 3 days 0.961, extrapolate that to 9 days 2.883

Ok it's not that much bigger...I just needed to keep my mind off my sinuses which are swollen up badly lol