kh ?

reefndude · Dec 8, 2014

Why does kh test lower in the mornings than it does in the evenings?
Does ph have something to with it, being that it is also lower in the mornings

Randy Holmes-Farley · Dec 8, 2014

If you are not dosing any, it should only decline.

Are you dosing?
What values do you observe?

reefndude · Dec 9, 2014

I use limewater

Mornings reads around 7.6

Evenings reads around 8.1

tyler1503 · Dec 9, 2014

reefndude said:
Why does kh test lower in the mornings than it does in the evenings?
Does ph have something to with it, being that it is also lower in the mornings

I could be totally wrong here and I have a very limited knowledge of the chemistry involved in reef keeping.
But the ph will rise throughout the day and drop overnight because of photosynthesis and oxygen depletion. I don't know exactly why. This will affect your kh readings. Fluctuations like this are normal. That's why you should always test at the same approximate time each day. If you have a refugium or frag tank plumbed into the same system you can turn their lights on at an alternate time to the dt to help fight this.
Like I said, I don't know enough to give a definitive answer, this is jut what I've pieced together myself. So take all this with a grain of salt.

reefndude · Dec 9, 2014

tyler1503 said:
I could be totally wrong here and I have a very limited knowledge of the chemistry involved in reef keeping.
But the ph will rise throughout the day and drop overnight because of photosynthesis and oxygen depletion. I don't know exactly why. This will affect your kh readings. Fluctuations like this are normal. That's why you should always test at the same approximate time each day. If you have a refugium or frag tank plumbed into the same system you can turn their lights on at an alternate time to the dt to help fight this.
Like I said, I don't know enough to give a definitive answer, this is jut what I've pieced together myself. So take all this with a grain of salt.

I normally test at nights. Times I've tested in mornings I would retest in evenings. Results are aalways consistent. Ph usually is 8.0 in mornings ro 8.3 in the evenings. I was thinking ph had something to do with kh readings.

Randy Holmes-Farley · Dec 9, 2014

Changes in pH from photosynthesis and respiration won't impact alkalinity, and alkalinity generally does not change with time of day except that it generally declines between additions.

If you are using limewater, then the alkalinity will change depending on the timing of testing relative to dosing. How are you dosing the limewater, reefndude?

If you are dosing in an ATO, you may have more evaporation during the day when the lights are on, delivering more limewater then and resulting in higher alkalinity.

Even if you add alkalinity evenly 24/7, since the demand need not be even through the day and night, you might get some cyclical changes in alkalinity if the demand for alkalinity is cyclical.

reefndude · Dec 9, 2014

Randy Holmes-Farley said:
Changes in pH from photosynthesis and respiration won't impact alkalinity, and alkalinity generally does not change with time of day except that it generally declines between additions.

If you are using limewater, then the alkalinity will change depending on the timing of testing relative to dosing. How are you dosing the limewater, reefndude?

If you are dosing in an ATO, you may have more evaporation during the day when the lights are on, delivering more limewater then and resulting in higher alkalinity.

Even if you add alkalinity evenly 24/7, since the demand need not be even through the day and night, you might get some cyclical changes in alkalinity if the demand for alkalinity is cyclical.

I use ato for limewater. My reservoir is open top, so evaporation is going on. I've been looking for another container. I have red sea and hanna test kits. Test results are consistent on both

Randy Holmes-Farley · Dec 9, 2014

Definitely close the top on the limewater reservoir, if that is what you mean. Even plastic wrap over the top would be good.

But using an ATO along with cyclic evaporation rates in the main tank would likely be why you see time of day changes in alkalinity.