Alkalinity demand dropped suddenly

[skidrow52]

I have a 150g mixed reef with a lot of SPS corals, I am also attaching my picture in this thread. I have been dosing 190ml of Randy's 2 Part Dosing Receipe 1 since several months and the Alk never went above 165-170ppm and CA 420-420ppm, but I used to observe a lot of precipitation happening in my pump impellers and in the sump due to which the pumps wouldnt start if turned off unless the impellers are cleaned every water change (bi weekly).

a week back I checked Alk and it was 197ppm which was pretty high and the CA was in the same range of 420-430ppm, I stopped the dosing pumps it dropped 21ppm in 24 hours (Hanna Alk) then I turned it back on and it jumped back 195+ppm, I understood the demand has dropped or the precipitation has stopped, i had let the dosing pump off for 2 days and let the Alk drop to 145ppm but the CA didnt drop, reduced the dose to 100ml and observed after 24hours Alk started increasing again, I reduced the 2 part dose to 70ml and checked after 24hrs there was again and increase of 4ppm, today I have reduced the dose to 45ml and will check exactly after 24hours how much increase or decrease is there and will set the dose accordingly.

I also noticed that after the water change I did 2 days back the return pump started normal without a need to clean the impeller like i used to do every water change.

IF the precipitation has stopped, why a sudden drop in Alk/Ca demand, yes I have noticed my frags were growing slowly if compared with my friends tank, these frags we receive on the same day, his frags are 3-4 times bigger in size than mine, I had very slow growth but the overall health of corals had been very good till today, the Ph has been always above 8 and even today its 8.02.

I am going for a 9 days vacation after a week and I am confused at what dose I should set it and leave.

I will appreciate your input.

 

[Boomer]

First skid, when you lose 20 ppm Ca++ you lose 50 ppm Alk. So, you may not even notice the drop in Calcium. Second a Alk of 170 is out of balance with your Calcium. NSW is only 115 ppm @ 410 ppm Ca++. You would better off at say 150 ppm Alk. Third, the reason behind the more normality after the water change is the tank is more in balance. Fourth, low Magnesium is the # 1 cause for drops in Calcium that do not add up. Have you ever checked that ? When you do that WC your raise up the Magnesium...BUT..that is usually what causes the Calcium to fall not stay more normal like you have.


I do not buy the accuracy of that Hanna at all and never have. That meter always seems to have accuracy issues. Tests have shown against std. it reads about 50 ppm to high. Meaning, your Alk is more like 120 ppm. So, your Alk may be lower than you think. Get a test kit to verify that Alk.


Since your Alk seems to be dropping will little drop in Cacium it is usually due to the Alk being used up by acids. When you do this WC, you reduce the acids and the Alk is more stable. If the Alk is being used up by acids it will lower the Alk to the corals slowing down their growth. Such acids are almost aways from over feeding, the tank high in dissolved organics, something dying or dead or a dirty tank.

1. Do two large WC.

2. Are you using GAC ? If not start using it.

3. Get a Alk test kit to check that meter against, as it reads to low. I would suggest a Salifert as it is a real seawater Alk kit unlike the rest.

 

[skidrow52]

Thanks for the reply in detail Boomer,

MG is above 1300 ppm (Salifert)
I did Alk test using Salifert test kit and the result was 8.0dkh and on Hanna 151ppm, exactly 24 hours before Hanna's test was 154 and then i had set the dose at 45ml.

Ph is goes upto 8 before the lights turn off, there is no drop in PH. Yes I am using HC GFO from BRS to keep PO4 below 0.03. I also did a test of Alk using API test kit and the result was 8 too.

I did 15% water change 2 days back, btw I am seeing growth tips on my SPS corals and the growth has become faster since I have drastically dropped the dosing, I am seeing the pumps working fine with no precipitation at all, trying now to stabilize Alk, I will keep increasing the dose as per the demand. Will do test every 24hrs for Alk.

Current tank parameters are
CA: 425ppm
Alk : 151ppm (Hanna) - 8.0 (Salifert)
Ph: 7.89
Temp: 25C
MG: 1335
PO4: 0.00 (Hanna)
NO3: 3-5 ppm (Salifert)



First skid, when you lose 20 ppm Ca++ you lose 50 ppm Alk. So, you may not even notice the drop in Calcium. Second a Alk of 170 is out of balance with your Calcium. NSW is only 115 ppm @ 410 ppm Ca++. You would better off at say 150 ppm Alk. Third, the reason behind the more normality after the water change is the tank is more in balance. Fourth, low Magnesium is the # 1 cause for drops in Calcium that do not add up. Have you ever checked that ? When you do that WC your raise up the Magnesium...BUT..that is usually what causes the Calcium to fall not stay more normal like you have. Lastly, I do not buy the accuracy of that Hanna at all and never have. That meter always seems to have accuracy issues. Tests have shown against std. it reads about 50 ppm to high. Meaning, your Alk is more like 120 ppm. So, your Alk may be lower than you think. Get a test kit to verify that Alk. Since your Alk seems to be dropping will little drop in Cacium it is usually due to the Alk being used up by acids. When you do this WC, you reduce the acids and the Alk is more stable. If the Alk is being used up by acids it will lower the Alk to the corals slowing down their growth. Such acids are almost aways from over feeding, the tank high in dissolved organics, something dying or dead or a dirty tank. 1. Do two large WC. 2. Are you using GAC ? If not start using it. 3. Get a Alk test kit to check that meter against, as it reads to low. I would suggest a Salifert as it is a real seawater Alk kit unlike the rest.
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