What is an acceptable daily alk swing?

recci

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I have a calcium reactor set-up and have it dialled in for 24-hour operation. I have been testing my alk twice a day, once just before the lights come on and once right after the lights go out and it seems that alk consumption is higher when the lights are on and lower when the lights are off as you would expect. It looks like there is a 0.4 dkh daily swing in alkalinity. It goes from around 8.3 to 8.7 during the 12 hours that the lights are off then from 8.7 back to 8.3 during the 12 hours the lights are on.

I have noticed some acro's showing signs of stress like the tips turning brown but not quite STN and I am thinking this could be the cause. But I can't see how it is possible to get it any more stable than that without computer-controlled testing and dosing.
 

redeyejedi

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It goes from around 8.3 to 8.7 during the 12 hours that the lights are off then from 8.7 back to 8.3 during the 12 hours the lights are on.
Is alk meant to raise when lights are off???? I didnt know that was a thing lol. It should be on a one way trip and that is down. Not up.
 

Zeal

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I have a calcium reactor set-up and have it dialled in for 24-hour operation. I have been testing my alk twice a day, once just before the lights come on and once right after the lights go out and it seems that alk consumption is higher when the lights are on and lower when the lights are off as you would expect. It looks like there is a 0.4 dkh daily swing in alkalinity. It goes from around 8.3 to 8.7 during the 12 hours that the lights are off then from 8.7 back to 8.3 during the 12 hours the lights are on.

I have noticed some acro's showing signs of stress like the tips turning brown but not quite STN and I am thinking this could be the cause. But I can't see how it is possible to get it any more stable than that without computer-controlled testing and dosing.
jFox did a presentation and said a .5 difference throughout the day wont make a difference
 
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recci

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Is alk meant to raise when lights are off???? I didnt know that was a thing lol. It should be on a one way trip and that is down. Not up.
Your corals consume more alkalinity when the lights are on because that is when they are photosynthesising. They still consume some alk when the lights are off but not as much. So if the calcium reactor is supplying more than is required in the dark it will rise.
 

Paul B

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I dose by hand (when I remember) and my alk swings way, I mean way more than that all the time. I doubt it makes any difference. Today it is probably about 6. I will go there and dump in a few ounces of alk to bring it up to about 8. That will happen over a time period of about a minute.

It is probably better to keep it stable but I have a lot of SPS and they are growing fine and my tank is very old as are all my corals. I wouldn't worry about point anything of a swing.
 
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recci

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I only mention it because i see signs of stress in some acropora. I know through personal experience if I did what you do and dosed by hand I would see issues. My alk drop from around 8 to 6.5 over a couple of days once and my acros all started to die. Other sps were not affected that i could see.
 
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jda

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I don't think that alk swing are the big of a deal, but I also don't let mine swing much or otherwise have issues. As long as my alk is the same at the same time when I test (evenings), then that works.

I have had alk get down into the 4s when I did not notice my co2 ran out. I bumped it right back up to high 6s with some baking soda dumped in all at once. No issues, but I don't do this all the time. I have no doubt that an alk swing could finish off an acro that was otherwise on the brink of a downslide.

FWIW, I keep a lot of what people call "hard" SPS that don't do well in other tanks... stuff that dies for some people. No issues. Not all acropora are the same level to keep... some are easier than others.
 

homer1475

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I'm with @jda on this one.....

If I forget to test, I can drop to 6.0 in a couple days. Instantly bump it back up to 7 and have 0 issues with any corals(LPS, Softies, SPS including several acros including a couple "difficult" species).

If a coral cannot withstand a 1DKH drop or raise in 24 hours, it was stressed to begin with and the instant increase in ALK pushed it over the edge. If your corals look stressed with a .5DKH increase, you have other problems that need to be worked out first.
 
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recci

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I'm with @jda on this one.....

If I forget to test, I can drop to 6.0 in a couple days. Instantly bump it back up to 7 and have 0 issues with any corals(LPS, Softies, SPS including several acros including a couple "difficult" species).

If a coral cannot withstand a 1DKH drop or raise in 24 hours, it was stressed to begin with and the instant increase in ALK pushed it over the edge. If your corals look stressed with a .5DKH increase, you have other problems that need to be worked out first.
I am unsure what the other issues could be. I dose nitrates and they are sitting around 10ppm which I am slowly bringing down to 5. Phosphate sits around 0.1. without dosing nitrate I would have a zero reading but a higher phosphate. I use an ATI power module so lights are not the issue.

Here some pictures of the acropora showing signs of stress.
 

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recci

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Over on the British ultimate reef forum, they say that a 0.4dkh daily swing is enough to harm sensitive acros and is pushing the limit of what will be successful long term. The reaction to my pics was those acropora are showing classic signs of "wobbly water".

Over there very few people run their calcium reactors 24h a day because when doing so, such a swing is inevitable. They recommend putting it on a timer to switch off for a portion of the night. So you aim to put 33% of the requirement through the reactor during the night, and the 66% during lights on. I am going to try switching the peri pump off for 15 mins every hour during the dark period and see what affect that has on my swing.
 

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