Your calcium is so low that maintenance doses will not really affect the balance that much. You should check the magnesium, but chances are good that will not be your problem. If mag where low it would allow calcium to gain control of the water chem and alk would be lower in most cases.
If you look at the
Seachem website it will give you a formulae for helping you with this problem......
Quote:
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Use 1 capful (5 mL) per 80 L (20 gallons).Each dose will raise calcium by about 10 mg/L. Size or frequency of dose can be adjusted, but do not exceed 25 mg/L per day.
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So 5 ml of product will raise the calcium by 10 mg/l in 80l of actual water volume.
Your 90g, calculated with displacement would most likely be closer to approx 75g (more, if a sump is being used), so needing to raise the calcium 140 mg/l would mean that you would need 18.75 ml of product to raise it 10 mg/l. Since Seachem advises raising the levels by no more than 25 mg/l in a day you can safely add 46 ml of product per day. That should have your calcium up in a few days. I would personally only do half of that, it will have less impact on the alkalinity. You should be safe with 25 ml of product per day. That would have your level up in about a week. I would also advise allowing the alk to fall off a bit. It will be a more balanced solution if the alk where closer to 11 DKH with a calcium of 400-420 mg/l.
Make sure you test the Ca prior to each addition and udjust the dose down if necessary. Once the alk falls down a bit you will need to maintain that as well. I find adding buffers more efficient in the AM, which will have less impact on the PH and Ca in the afternoon. Depending on tank GPH, that will give you less concern of precipitation.
I would also suggest bringing down the SG. Depending on the tank temp, it will in most cases have an actual higher value unless using a refractometer which measures the salinity and is not affected by temp if calibrated properly... You can check
here if you do not.
Cheers
Steve