View Full Version : alk fluctuations during a 24 hour period

12/28/2015, 10:29 AM
I haven't had enough growth to know if this is normal or not, but i have my doser set to dose the tank once an hour for a 24 hour period, but i've noticed since the increased growth, in the morning the alk is at 9, after the day right before lights out it's at 8.5, and then back up to 9 in the morning. Is this normal? Should i try and stabilize it more or is that alright, and what kind of apex code would make my doses more in the day and less at night if needed? ph usually goes from 7.85 or so in the morning to 8.2 during the day.

12/28/2015, 11:33 AM
You could try to tune the dosing rate, but I'd just ignore that variation. That's a very small range, and probably close to the accuracy limits of the kit. I don't know how to program the various controllers, but it might be easy enough to do as a fun project.

12/28/2015, 11:53 AM
I always hear about wanting stability, so figured i'd ask. It's a hanna tester, i've done some tests back to back and usually get the same number or one off, so pretty accurate in my opinion. The readings in the mornings and afternoons are consistent.

12/29/2015, 10:24 AM
I do the same. At least in my tank, the trend seems to be that during the lights off period, alk does not drop, and during the lights on period it does. I've observed this several times when allowing my alk to drift down naturally with the dosers off. That's why its important to check it at the same time each time. In the evening it will always be lower than in the morning, but from day to day it is consistent. I think that's what you want. Trying to modulate them to be consistent over a 24hr period just sounds daunting and needlessly complicated. Its no different with Ca reactors. They output the same constanty over 24hrs. Also please be sure that your expectations of "growth" are realistic. I find many do not know or appreciate how slow corals grow at the beginning.

12/29/2015, 11:26 AM
I've been watching stagnant growth for 6 months + until i made some changes when i realized what was going on, I'm getting all my colors back and growth tips. For me, growth tips are my only expectation, lol, that and encrusting. I was measuring twice a day as as soon as i made a change in the amount of lighting, almost immediately my ph shot up, when i see something change like that i monitor everything else, and alk took a nose dive, and i've been adjusting and now at the point of fine tuning again, so my testing is daily now and soon to be every other day and then back to weekly. I just didn't know if that daily swing was normal or not, that was my only real concern, if that happens in all tanks, no worries for me here.

12/29/2015, 08:51 PM
Some swing is normal. The corals grow at somewhat varying rates during the day, so the demand is a bit variable.

12/29/2015, 09:57 PM
I dose my 2-part hourly to during the photo-period. Figure this is a good compromise.

I saw a very noticable increase in growth rate once I got the Alk levels to remain constant on a week-to-week basis. If I measure at the same time of day, I expect Alk to be the same (within measurement error).

I have not tried to measure the intra-day rate but I think thats going too far. Measurement errors are likely to prevent us from making adjustments that are substantially better than shooting for stable level at (say) 6pm every day.

Measure the Alk but please ignore your pH readings. pH is more a function of dissolved Co2 than anything else and your range is fine.


12/30/2015, 07:36 AM
I was told he changes throughout the day with the temp and lights (don't know how true that is). My LFS told me that every time you do a test no matter what it is; is to test at the same time of the day to get an accurate reading. I always test at 6pm. Try testing one day at a certain time and test the next day at the same time.

12/30/2015, 11:18 AM
How much of a variance would you allow before you think there is a problem? Say I test at the same time everyday but my alk readings are 9.6, 9.4, 9.7 eg.

12/30/2015, 08:51 PM
How much of a variance would you allow before you think there is a problem? Say I test at the same time everyday but my alk readings are 9.6, 9.4, 9.7 eg.

If your readings are that close you're done! And, by the way, you're a testing god! Enjoy a festive drink and your tank!

The real answer to your question would be quite technical and depends on your test kit and methods. Practically speaking, I'd ignore anything +- 0.5 dKH or so.

Stability is more important than the number. So test again 3 or 5 or 10 days later. If those numbers are also within +- 0.5 dKH you're good. If there is a definite trend higher or lower, adjust accordingly.

Water changes will affect Alk too, the larger the PWC, and the greater the difference between your make-up water and DT water the more your Alk will change with a water change. Choosing a salt mix with an Alk level the same as your DT level is one way to ensure stability. Continual water changes is another.