2-part dosing help please

[ZeeSparrow]

My 75G tank had the first coral added in May of this year, shortly after cycling. Small frogspawn and candycane from a local reefer. Since then, I have periodically added a few more frags every few weeks for a total of 13 LPS and 4 SPS (birdsnest, monti cap, pavona and turbinaria).

Alk had remained relatively stable around 8.3-8.6, with calcium 400-420, while mg started depleting in July (down to 1200). I initially used Kent Tech-M to raise it up to 1350, keeping it above 1260 with an occasional squirt. Salinity typically 1.025 (calibrated refractometer), temp 77.4-79.7.

Last month, Alk was 7.3 so I started dosing using BRS supplements. I initially mis-calculated (using meq/L rather than dKH) and added a bit more Alk than planned, but there were no harmful effects noted.

Here's a summary of the past two weeks:

9/9 5:00PM - 9.6 dKH / 430 Ca - added 7ml each
9/10 7:00PM - --------------- added 10ml each
9/11 --------------- added 7ml each
9/12 --------------- added 7ml each
9/13 --------------- added 7ml Ca only (forgot alk)
9/14 5:00PM - 10.8 dKH / 410 Ca - added 7ml Ca in the AM, 3oz after testing (no alk)
9/15 8:00PM - 10.9 dKH / 420 Ca - added 2oz Ca (no alk)
9/16-9/18 - no testing or additions
9/19 7:00AM - 8.6 dKH / 440 Ca - added 16ml each (per BRS calculator - 32ml needed to maintain 0.66 estimated usage per day)
9/20 5:00AM - --------------- added 16ml each
9/20 7:00AM - 12.2 dKH / 430 Ca (CRAP! - no more additions)
9/21 4:30PM - 11.4 dKH
9/22 4:30PM - 9.6 dKH
9/23 6:30PM - 8.6 dKH / 430 Ca

Birdsnest and duncan were the only coral to show effects of the high Alk. As of yesterday, they are both open with PE.

My plan is to test Alk again tomorrow night. If the current rate of consumption continues, that will put it below 8.0. Per BRS calculator, that's a whole lot more than the 32ml I dosed last week... which I'm hesitant to even consider. I'm thinking maybe if I dose 10-15, then test an hour or so later, I can verify the effect. Then repeat that procedure for the following nights until I am comfortable with the adjustments being made (i.e., test, dose, test again until the calculator and my tank agree).

Sorry for the long post but I wanted to include as much info as I thought might be relevant...

Thoughts/suggestions?

 

[dkeller_nc]

When setting up dosing for the first time, don't use a calculator to determine each dose. Instead, test after three days, determine your tank's usage, and divide that into 3rds. Start adding that amount of Ca and Alk solutions each day, and re-test after 3 days, 6 days, and 9 days. Make small adjustments to the amount you're adding depending on your 3, 6 and 9 day test results.

Make only small adjustments - don't rapidly change the amounts. The reason is that Ca and Alk tests aren't terribly precise; the best you can hope for is +/- 0.5 dKH Alk and +/- 20 ppm Ca.

 

[ZeeSparrow]

That's what I'm trying to do, I think. Three days ago, a Alk was 11.4. I'll test again tonight. Let's say that result is 7.8. That's a drop of 3.6, average of 1.2 per day.

To know how much solution to add, I use the BRS calculator. From 7.8 to 9.0 dKH on 80 gallons it says I need 68.5ml.

But when I added half that amount my Alk raised from 8.6 to 12.2. ??

So... How do I know how much to add?

 

[biom]

if 7ml worked for you (even was a little bit more) why you are going to increase (double) the dose? I will go for 6 ml and test.

 

[hkgar]

When using a calculator to first set up dosing you need to know the actual amount of water tanking into consideration the gallons displaced by sand, rock and the space between top of water and top of tank.

I have a 180 and 40 sump but actual system water is about 171.

Here is a link to a good calculator for tank volume

http://reef.diesyst.com/volcalc/volcalc.html

 

[bertoni]

When using a calculator to first set up dosing you need to know the actual amount of water tanking into consideration the gallons displaced by sand, rock and the space between top of water and top of tank.

Yep, that's generally the problem. You could chart the change in dKH from a dose, and compute back to the volume of the tank. Over time, that'll get you close enough.

There's no point in measuring calcium all that frequently. The noise in the test is probably at least 8 ppm, so two reading that differ by 16 ppm could correspond to the same level of calcium.

 

[ZeeSparrow]

Yep, have that site bookmarked.

Alk tonight is 8.6, same as last night. Refractometer was off though - recalibrated and tested salinity at 1.024. Turned off ATO and used about half a gallon of saltwater to top off, bringing it up to 1.026. That's going to throw things off.