Is my CO2 really bottoming out?

[jsoong]

OK, this is my 2wpg, non- CO2 planted tank that was completely relandscaped 3 weeks ago. I am noticing an increase in algae (dark green, covering & almost smoothering plants )

I did a bunch of water tests last nigh & noticed a very high pH (8+ may be 9 -- can't read very well at such extremes!)

My tap has pH of 7.8, KH of 100. I tested GH & KH in tank & they are unchanged (if anything KH is a bit LOWER).

The sample was taken just after lights out, so I am wondering if low CO2 is to blame. This am, just after lights on (when CO2 should be replenished) the pH is back to 8.

I can only conclude that my CO2 (which was 3 - normal - at the start of the day) had bottomed out to less than 0.1 at the end of the light cycle. I always thought that with a wet/dry, the CO2 should be well equilibrated with air & stay at 3 all day. Can my plants (or algae) be that efficient in removing CO2 to bottom it out like that?

 

[fish_4_all]

If you are not injecting CO2 then you need to agitate the surface of your tank to replenish the CO2 and O2 levels. This should keep it about 3ppm most of the day. A bubble wand, your HOB splashing or an airstone should provide all you need to keep the balance.

 

[czcz]

Wow, it is surprising if CO2 is taken up faster than the wet/dry replenishes it. I bet its possible with enough plants though. If I remember correctly Steve Hampton wrote some stuff on plants taking C from KH with CO2 limitation, so perhaps your KH trest verifies this.

What's your lighting like again? Already started no-CO2 EI? Any chance of using some floaters in the main to block light and grow with atmospheric CO2, to outcompete the algae? Do you already have high plant mass?

I figured a non-CO2 appropriate tank with wet/dry would do great. I bet with some adjustment it'll get there.

 

[JRagg]

Only certain plants can take the C from the KH. I want to say vals are one of them, but I've read that in a book as well.

 

[Wizzard~Of~Ozz]

vals and anacharis are the 2 that I know of. this is evident from their reaction to Seachem Excel. (It inhibits their ability to extract C from KH from what I remember)

 

[Zezmo]

Perhaps something else is affecting your Ph? If I read your post right you are asking about the CO2 bottoming out becasue your Ph is higher than expected. It is possible that something else is buffering your tanks Ph or otherwise affecting the test.

 

[7Enigma]

Algae/bacterial blooms are known to cause increased pH in tanks. You mentioned that you have a lot of algae now, this could definatley be causing the increased pH (but there are many other possibilities as well).

I don't think your CO2 levels are the cause for your pH changes, as 3ppm will not swing the tank pH as drastically as you are seeing.

Also buy a pipet or use a piece of hose or a turkey baster and take your water samples from the center of the tank that gets average flow (ie not right at the outlet of your filter, nor in a low flow area). When measuring pH it is very important that you are not pulling surface water as it will have the most variable pH level (due to the CO2 going in and out of the water depending on equilibrium levels).

What is your KH level?

 

[jsoong]

I am quite surprised that the CO2 can bottom out in a wet/dry system ... that's why I am posting this for more insight.

I don't think that the pH change is due to some kind of dissolved buffer .... after all the KH & GH did not change & the pH increase reversed overnight. The only thing I know of that will cause a reversible pH swing in sync with the light cycle is CO2 level change.

Currently the KH is about 100 ... which gives me a CO2 of around 3 with a 7.8 pH, and 0.1 with a pH of 9.

Although I have something like 20-30 plants, I would not call this high plant mass ... since the tank had jsut been re-done & most of the plants are quite small. The light is 4x32 W T8 (~2 wpg). The algae seemed to be doing quite well - covering a lot of the rocks & plants - but strangely, not much on the glass. Whenever the lights are on, there is quite a bit of pearlings from the algae ... so I am sure that it is consuming a bunch of CO2.

ATM, I am going to watch this tank for a few more days .... good idea on getting a water sample from deep in the tank ... will try that. To combat the algae & to give the new plants a chance to get established, I think I am going to do either a blackout - or to turn off 1/2 the lights for a while.

BTW, I am dosing ~ 0.05 ppm of Fe (& trace), 3-4 of N & K & 0.5 of P each week. I have noted the nitrates bottoming out after 4-5 days (will try splitting the dose in 2 & dose 2x a week). I guess I still have a lot to learn about getting it right with my setup .....

One note on Vals & their ability to get C from HCO3. In my tank, the vals are growing the best ... evidence of their ability to thrive in very low CO2 environment?

 

[7Enigma]

I like to dose my tank to 20ppm nitrAte to be sure they never bottom out. At this level your fish will have no ill effects. Then dose your phosphate a bit higher as well. I go by the thinking that its always better to have slightly MORE than you need then risk bottoming out on something.

 

[Steve Hampton]

I don't think your CO2 levels are the cause for your pH changes, as 3ppm will not swing the tank pH as drastically as you are seeing.

It depends on what the beginning CO2 levels are...meaning, if your CO2 levels are 30ppm then no a drop of 3ppm to 27ppm won't cause a move in pH. But if your CO2 is 3.1ppm and drops to 0.1 the change is pH is huge...check the CO2 charts for reference.

This is the start of biogenic decalcification. In this case jsoong probably won't develop full brown biogenic decalcification because it requires intense lighting but the makings of the condition has started. Scale or calcium carbonate marl would form on plant leaves as the next sign.

Back to the issue at hand. IMO this is definitely related to the plants and more directly the algae stripping C from BC. Algae are much more adept at stripping C from BC...that is why they have an advantage in a CO2 limited environment.

Jsoong, normally I'm not a fan of the "siesta" period for lighting as I believe its an unnatural approach to start and stop photosynthesis for plants...but in this case a "siesta' period would likely solve your CO2 limitation. Breaking the photoperiod in half with a few hours rest in between would give your tank a chance to "rebuild" CO2 halfway through the lighting cycle. While its doubtful the "siesta" period is effective at algae control the way some people have reported it to be, in certain CO2 limited situations such as this I think it could be a real help...if your willing to test.

 

[czcz]

Do you think increasing flow rate through the wet/dry would adequately replenish CO2?

BTW, I am dosing ~ 0.05 ppm of Fe (& trace), 3-4 of N & K & 0.5 of P each week. I have noted the nitrates bottoming out after 4-5 days (will try splitting the dose in 2 & dose 2x a week). I guess I still have a lot to learn about getting it right with my setup .....

Dosing the same amount twice is reasonable under non-CO2 EI I think, or just bump up the amounts some after halving it. I think its wise to do this: If the tank bottoms out on nutrients now, likely it will faster with atmospheric CO2 available. HTH

 

[Zezmo]

I know in this thread we are talking Co2, and Ph etc..... However in rereading Jsoong's description of the algae in his tank, could he be dealing with BGA instead, and all this other stuff is incedental.

 

[jsoong]

Steve - Biogenic decalcification - I think it is happening in my tank - I am seeing a layer of white stuff on some of the rocks ... this must be CaCO3. For those interested, the KRIB has a good discussion on this: http://www.thekrib.com/Plants/CO2/decalcification.html

Zezmo, I don't think I have BGA ... The algae is looking more like BBA that I had before.

I have adjusted the water return from the sump to get more surface aggitation, and this seemed to have moderated the pH change somewhat (instead of going from 7.8 to 9, it is swinging from 7.8 to 8.5 or so).

I am still amazed at the amount of CO2 consumed. If my wet-dry is 100% efficient in equilibrating the water to air, then at 600 ghp flow, the tank is consuming something like 5-6 g of CO2 per hour. I rather doubt that, so maybe I'll fiddle with the filter to get better air mixing.

I think I will do a 48 Hr blackout this WE, then I will try the interupted light cycle as Steve had suggested & see what happens. I am almsot at the point of trying CO2 (maybe DIY to start), but seeing all the pics of the beautiful non-CO2 tanks that the members has, I'll keep trying for a while longer.

 

[Steve Hampton]

Personally I have complete faith that if you set your mind to it you will succeed with the non-CO2 approach...you just need to find the sweet spot. Once the algae is controlled the CO2 demand will lessen a great deal. The blackout should help but it won't kill all the BBA...if its actually a form of BGA then the blackout likely will kill the BGA. Either way, the decaying algae (or bacteia in the case of BGA) will pollute the tank and so a large water change is needed after the blackout. I'd also add a word of caution about doing the blackout with some combinations of fish. A tank with a nocturnal predator or very aggressive fish may swing the tide in their favor during the extended blackout time. As much as I've preached about the blackout being safe, I now have seen enough reports from trusted hobbyists that have lost fish that some caution in evaluating the fish species is a prudent idea.