Chamistry of alkalinity

[Treefer32]

So, my toadstool and GSP wouldn't open for a week. I couldn't figure it out, alk with hanna checker was always stable at the 7.8 to 8.2 range, calcium 450, nitrates 16, Some phosphates but I have an algae scrubber. So really hard to know the value of phosphates / nitrates.

Salinity 1.026 (first time I got it with a water change from 1.025 to 1.026. I was so proud of myself, but then the corals that let me know if something is wrong didn't like the water change. I let them go a week, just thinking they were moody at the slight temp change of the water change, or slight salinity change or something. 10 days went by, still not open. I was almost out of Hanna reagent so I bought a new bottle and used a new bottle. It tested at 13.5. My old reagent had become contaminated with oxygen or salt water or something and was reading 70% lower readings than reality.

So,slowed my doser way down to allow the alkalinity to naturally drop. Over the course of the last 6 days and only dosing fresh water right now with the doser (just letting it run because I need to keep my calcium up). 6 months ago with less corals, I was consuming close to 2-3 dkh a day.

That said, it's dropping around .2 to .5 dkh a day. On average maybe .3 dkh in a 24 hour period. Still running my skimmer and algae scrubber.

Yesterday afternoon I was down to 11.2, starting into a more normal acceptable range. My GSP and toadstool both have started opening about 1/4 of the way now that it's under 12. I would prefer it get to 9. But does consumption slow if concentrations are too high? That appears to be the case for me, but just curious if the behavior of reduced growth / consumption of both corals and coraline is a result of it being too high? A cascading issue if you will.

I can't do a water change until the alkalinity is within 1 dkh of my water change water and so I'd need to raise the alk of my water change water to be 1 dkh lower than my tank (around 10) or wait until the tank drops to 8 -9. I use IO salt. So, it generally runs low in alk. My last batch was really high in MG and low in alk. go figure.

My calcium was reduced from 460 to 380 when I slowed my calcium dosing down. So, I know calcium is still being consumed despited the slowed alk consumption. My tank's magnesium tests at 1550. And I don't dose magnesium. This batch of IO tests the same as my display, so around that 1520-1560 mark.

Anyways, just curious why alk is dropping so slow, when it's normal, it drops rapidly.

It's a 340 gallon display with 75 gallon sump.

 

[Randy Holmes-Farley]

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Anyways, just curious why alk is dropping so slow, when it's normal, it drops rapidly.

It is normally true that the higher alkalinity is, the faster it drops, with it nearly stopping the drop when it gets down into the 6 dKH range.

A sudden rise or fall may disturb corals and they may reduce their demand for that reason.

many corals thrive and even grow faster at higher alkalinity than at low alkalinity, so I would be wary of attributing all the issues to alk at 13 dKH.

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I can't do a water change until the alkalinity is within 1 dkh of my water change water and so I'd need to raise the alk of my water change water to be 1 dkh lower than my tank (around 10) or wait until the tank drops to 8 -9. I use IO salt. So, it generally runs low in alk. My last batch was really high in MG and low in alk. go figure.

Doesn't make sense to me. Normal IO has alk around 11 dKH. maybe it was a bad batch (if you thought it was lower), but more likely your testing was reading it low (IMO).

Anyway, even if somehow the new salt water you have is really only 8 dKH and your tank is 11 dKH, a 10% water change will only drop alk from 11.0 to 10.7 dKH, which is an OK drop.

 

[Randy Holmes-Farley]

My calcium was reduced from 460 to 380 when I slowed my calcium dosing down. So, I know calcium is still being consumed despited the slowed alk consumption.

Anyways, just curious why alk is dropping so slow, when it's normal, it drops rapidly.

Calcium can only be consumed along with alkalinity, at a rate of about 18-20 ppm calcium for each 2.8 dKH of alk.

If alk consumption is way down, and you are not adding it some other way (like using tap water), then the calcium consumption must also be way down.

 

[Treefer32]

As to other causes of my GSP and Toadstool not opening, I've seen 2 of my tangs eating stuff off the GSP. I assumed it was leftover food or something. A chocolate tang and a Caribean blue tang are the main culprits. I moved the GSP rock about 2 inches. It might be getting more light.. So, it could just be mad and the Alk changes just made it want to stay in hiding for a bit. Same with the toadstool it got moved.. Probably doesn't like it's new spot. It stung a few times by my stunner chalice. It looks to be healing.

I retested alk yesterday afternoon about 24 hours. PH was 8.33, Temp 78.2 and alk came out to 11.1. A .1 dkh drop in a 24 hour period with no dosing. My top off water is water that first goes through a water softener, then through a BRS 150 water saver RO unit (with both RO membranes recently replaced - were both 6 years old). The water coming out of the RO unit is around 3-5 TDS. The water out of the DI is 0. I have a 75 gallon top off bin. The water in there lasts close to 2 months. It's not circulated or kept oxygenated. I would estimate my top off at around 1 - 1.5 gallons a day. Salinity is staying stable at 1.025.

I was hoping it would drop by more than .1 dkh per day. I'll do a water change this weekend and test the new saltwater to see where it's it at for alk. Can I use Vinegar or citric acid to reduce the alkalinity of the new water if it's still around 9 dkh or so. I'd really like to get it down to 10 after the water change then let it come down by .1 a day if it wants.