pH Trend with CO2 injection

[sessionthree]

Hi all,

I have a 120 gallon tank that I just planted about 1 week ago (fairly heavily). I have some questions about CO2 injection and pH trends over time, but first some facts about my tank:

• Lighting: 4x54W T5HO (2xAquaMedic Reef White 10k and 2xAquaMedic Plant Grow 6500K) - currently only running 2 bulbs until max CO2 limit is found (8 hour photoperiod)
• Filtration: 1 Fluval FX5 plumbed to the built-in dual overflows of my aquarium
• CO2: 20lb pressurized CO2 with solenoid, currently turning on CO2 2 hours before lights and turning off 1 hour before lights out, CO2 is injected into the input flow of the canister filter
• Substrate: Eco-complete, ~2-3 inches in front and about 4-5 inches in back with Osmocote Plus Rootabs inserted
• Fertilizer: Follow EI schedule with KNO4 (1.5 tsp), K2SO4 (0.5 tsp), and KH2PO4 (0.5 tsp) on Sun,Tue,Thu, Plantex CSM+B (0.5 tsp) on Sat, Mon, Wed, and 50% water change on Sat.

For several days after I got the plants in, I had heavy pearling because I kept the CO2 cranked up 24x7 (no livestock to worry about) and I had all 4 lights on. My drop checker was indicating a mellow-yellow type color. However, I developed a bit of a case of Rhizoclonium so I decided to reduce lighting to two bulbs until I found my optimum CO2 since my research suggests that Rhizo is from too much light and too little CO2. Now, I'm running CO2 during the day with the lights (on 2 hours before lights and off 1 hour before lights go out). I have 5 Ottos and a couple of Bulldog Plecos in the tank, so I'm hoping they can help me find the optimum, maximum CO2 for the plants before causing stress on the fish. Since reducing the lighting to 2 bulbs and moving to CO2 off at night, I'm not noticing near as much pearling.

Here's a chart of my pH over the last few days:

The blue line is my pH and the red line is the on/off state of my lights. You will see slight inflections in the pH curves while the CO2 is on as I'm slowly increasing my bubble rate each day (I didn't adjust during the last CO2 on period). My question is in relationship to the pH and how long it takes to stabilize in the CO2 ON and OFF cycles. With CO2 on during lights ON, I'm not seeing the pH stabilize until 4.5-5 hours until after lights have been on. During the period when the lights are on, I do observe that my drop checker is a light green at the start of the period and a mellow-yellow color at the end of the period. With CO2 off during the night, pH doesn't stabilize at all really. It increases throughout the period until CO2 turns back on the next day. It does show a slow-down as if it is reaching an asymptotic limit, but never gets there.

Note, I'm not using pH to control CO2 at all. I tried that first and realized that was a bad plan since my KH changes before/after the weekly water change and would affect the pH vs CO2 relationship. I've noticed about 7-8 dKH after a water change and 10-11 dkH just before a weekly water change. I'm just using the pH for observational purposes.

My questions:
1) How much lag exists in measuring pH with a probe vs how much CO2 is actually dissolved in the water column? I'm assuming it is very low lag since I see immediate pH changes when CO2 turns on and off.
2) If the lag is low, does this mean my diffusion method (CO2 into the canister) isn't up to snuff since I'm not getting stability in the pH until 4.5-5 hours after the lights have been on (6.5-7 hours after CO2 on)?
3) Also if the lag is low, does this mean that the slow stabilization of pH at night means that my outgassing of CO2 from the water at night is slow? I've got significant surface agitation from the return of the canister filter plumbed through the returns drilled through tank. The surface ripples pretty well across the entire water surface.

I want to convince my self to not worry so much about what the pH is doing unless it really is telling me about a deficiency in my setup.

Thanks,
Clayton

 

[Tom Barr]

New tank and all............

I'd likely drop the pH down a full point(you are dropping about 0.7-0.8 pH units now) and add some sort of surface scum extractor.
The middle 2 waves look decent.

You might keep the lower light for another week or two, then try more light later after.
The 1st month, I'll do 2-3x a week water changes, 60-80%.
Till those plants are established and growing well............the system is very unstable.

1. in my 120, I see a somewhat similar lag trend, but the CO2 moves faster.
We only use one pH probe and one point to measure. If you shake the probe, often the pH will drop or rise.
They make pH and probe shakers for measuring dissolve gas in water systems for this reason.
Try it and see, move the pH probe around and allow it to settle.

Try it in the lowest flow spots, in the plant beds, corners and then right next to/in the filter flow etc.

 

[sessionthree]

New tank and all............

Yes, indeed. And also absent from the planted tank hobby for 12 years or so. Back then, I was doing DIY CO2 on smaller tanks, but had quite a bit of succcess. Since then, I experimented for 2 years with a reef tank, but decided to get back into planted tanks. The whole reef thing doesn't suit me as well for some reason. I like the beauty of green, I guess. (Although, I did think about doing a Macroalgae reef tank - and sort of did for awhile due to all the beautiful macro algae I ended up with on some live rock.)

I'd likely drop the pH down a full point(you are dropping about 0.7-0.8 pH units now) and add some sort of surface scum extractor.
The middle 2 waves look decent.

Was trying to reach the 1 pH point drop, but maybe I'm going too slow in increasing the bubble count each day. I'll be a little less timid, though, and try to increase the needle valve a little more each day than I've been doing. I'm also working on my ATO float switch level so that I get a slight drop in my overflows to make sure I'm cleaning off surface scum.

You might keep the lower light for another week or two, then try more light later after.
The 1st month, I'll do 2-3x a week water changes, 60-80%.
Till those plants are established and growing well............the system is very unstable.

Will do.. still EI dosing while doing these, I assume?

1. in my 120, I see a somewhat similar lag trend, but the CO2 moves faster.
We only use one pH probe and one point to measure. If you shake the probe, often the pH will drop or rise.
They make pH and probe shakers for measuring dissolve gas in water systems for this reason.
Try it and see, move the pH probe around and allow it to settle.
Try it in the lowest flow spots, in the plant beds, corners and then right next to/in the filter flow etc.

I remember the difference in pH measurements if I shook the probe with my reef system. Right now, I have the probe zip tied to a pipe in one of my built-in overflows. I'll move it around to see what kind of results I get.


Thanks for the response. I have a little more confidence now. I'll increase my water changes and continue to increase CO2.

-Clayton

 

[sessionthree]

Just a quick update...

I upped the CO2 so that I'm getting a full point in pH drop during the day, and I really like the results. Not only am I getting the full drop, but it's also getting there faster after CO2 is turned on. The pH curves look much better.

I also plumbed my tank to a downstairs utility sink so that I can quickly do water changes with the twist of a few valves. My weekend project involved putting automatic sprinkler valves so that I could automate water changes, but yeah... that didn't work out - long story! Oh well, manual valve turning is fine and I'd rather be there when I'm doing water changes anyway!

Last night I turned off my canister to do a water change and good grief, there was so much pearling. Streams and streams upward bubbles everywhere - beautiful sight. Plants seem to be happy with the CO2 setting I've found even with one set of lights on. Now to just keep up with the water changes and manual removal of the Rhizoclonium until it stops growing!

 

[Gerryd]

Hi,

but maybe I'm going too slow in increasing the bubble count each day. I'll be a little less timid, though, and try to increase the needle valve a little more each day than I've been doing.

You can never go too slowly or be too careful with c02...It is a killer...

Note that sometimes it takes more than a day or several hours for the effects of the increase are all known. With a canister setup you will retain more c02 into the non light periods and still have a lot in the morning.

Keep an eye on your fish and critters as well during the photoperiod to ensure all is well while c02 is on.

Try turning the c02 off one day for 20 mins or so and see if they behave differently. Extra surface ripple and 02 during c02 injection provides a nice safety net for all.

 

[Tom Barr]

Regarding automated water changes, you can use an auto float switch for the refill, then use a small pump, saya Rio 90 etc to pump water out and have an air gap between the hose and the drain from this.
Say the pump sends 50 Gal in 30 minutes out down the drain, the float switch fills the sump up with pre warmed tap water ran through a carbon block filter, eg a 20" x 4.5" dia carbon block prefilter.
This changes daily on a simple peg style timer.

Add a pair of dosing pumps, then daily dosing is done as well.


Most of my tanks have about 1.2 to 1.4 pH drops.
But they have surface skimmers and large wet/drys etc lots of current etc.

 

[sessionthree]

Most of my tanks have about 1.2 to 1.4 pH drops.
But they have surface skimmers and large wet/drys etc lots of current etc.

Well, I've been going slow increasing CO2 and I hooked up a webcam so I can monitor fish while at work and turn off CO2 remotely (via Apex) if I ever see signs of fish stressing. So far I'm at a ~1.3 pH drop. Thing is.. I'm running a canister filter, so I should have a more difficult time with DO. I do have the returns from the canister creating some good waves on the surface, though. I also slightly lowered the maintained water level in my built-in overflows that feed the canister so that the surface is skimmed well. Where before I was getting a bit of a surface scum due to the water not dropping enough in the overflows, I have no surface scum now. (I took out the standpipes, so the canister is just plumped such that the water is draining from the bottom of the overflows to the canister.)

So, 1.3 pH drop and still no signs of fish stressing. I guess I am getting enough oxygen in the water. I'm actually getting a little concerned about pH levels in general, though. I did a water change last night and right before CO2 turned on today, my pH was at 6.91 (the max pH drops a bit after water changes and rises a little each day until the next water change). Here it is about 30 min before CO2 off and the pH is at 5.61. In my first post, the max pH was higher, but it has lowered over time. My tap water at that time had a kH and gH in the 5-6 range, but just since then my tap water gH and kH has lowered to about 3. So, that probably explains that. I'm going to start adding a bit of gH booster at water changes, and perhaps boost kH a bit, too. I have some vals that are really growing like weeds, so I'm sure they are using some of it up. (Not sure why the pH rises slightly from day-to-day, though, if that's the case.) I've calibrated my probe several times (and verified measurements in standards), so I'm confident my pH is reading correctly. It sure doesn't jive with my API test kit, though. I also verified that the API nitrate test sure isn't reading correctly either by measuring a standard solution that I made. I think I'll throw that whole test kit out the window. Oh, speaking of throwing things out the window... that drop checker that was reading yellow with a 0.8 pH drop, yeah.. how misleading. I might have had a bad 4 dKH solution, but forget it. I'll just look at plants and fish for now on.

Since you mention a max of a 1.4 pH drop in your tanks, I'm a little nervous about increasing CO2 any more. I'll leave it here for a few weeks to see how things go. So far, the plants are growing like the weeds they are.

Oh, and I ended up cheating a bit and using Algeafix to get rid of the Rhizoclonium. Wow, did it work! No Rhizo at all after the 3 day treatment (as prescribed on the bottle), and it has been about 2.5 weeks since treatment. I think that one blast to get rid of it and the corrections to get CO2 increased has helped it to stay away. I'm a believer that it's mostly about the CO2!

I'm probably going to keep up the twice per week 50% water changes at least for another 2-4 weeks. Then, I'll move to once per week assuming everything continues to do well.

Thanks and sorry for rambling!

-Clayton

 

[sessionthree]

Ok, I spoke a little bit too soon. After more careful observation, I noticed an increased breathing rate in some of my fish. I even had a rubberlip pleco who had stopped breathing and wasn't moving. I gently poked him a bit and he would start breathing slowly again. I continued to do this until he would finally move. Eventually he made it out ok, but he was definitely out cold and probably on his way to death. So, I'm back to a 1.2 pH drop. With this CO2 level, I still see good pearling and growth and don't see signs of fish stress. I'm sure with a wet/dry I could probably get more CO2 in, but I'll see how things go here before I start changing things.

-Clayton