ph profile for 230l tank - confusing results

[TrevC]

Hi - 4 months into my first tank and I wanted to check my CO2 injection performance by compiling a pH profile through the daily cycle. I was pretty convinced that I was lightly dosing the CO2 with only 1.3 bps and drop checker showing green (not light or lime). I read the excellent posting on this forum at Dialling in the CO2 injection Rate and CO2 Profiles My impression is that this profiling is simpler for smaller tanks but the daily cycle could be more difficult - and the needed pre-light injection period substantial for my size of tank.

My tank basics are:

1. 90x60x50 cm so about 230l
2. Hardscape: lava rock, driftwood, fluval stratum in bags below riverbed sand.
3. Filter is Betta 1040 UV with charcoal, Matrix and Purigen media
4. Filter outflow is a spraybar running the length of the tank
5. CO2 system is CO2 Art with in-line diffuser
6. Basic TNC Complete dosing and JBL Kugeln clay balls using in front substrate.

First I read pH for the current situation. Lights on 13:00 - 21:00 and CO2 started 2hrs previously at 11:00. Before CO2 came on the pH was 7.4 and didn't change much all day except dropping to 7.2 by about 16:00. This confirmed my light dosing suspicion.
Next day I used a bubble rate of 2.5 per second and a pre-light injection period of 5 hours with the attached resulting profile

It shows a pH drop prior to lights on of about 1 and a steady level during lights on - so early signs good. However, there are some confusing issues:

1. it appears to takes a long time for degassing - at midnight (3 hrs after lights off) CO2 was still at 6.5. By 7:15 the next morning (just prior to CO2 coming back on) it was up to 7.0 but not fully restored to 7.4 as previous day. With a long time to raise pH and slow degassing I was concerned about pH drops becoming cumulative over multiple days
2. Really confusing was that my reference sample (removed from tank and let stand for 24 hrs) showed a pH of 8.5. I had to use a regular ph test because this was outside the scale of the narrow range test. Tap water tested at 7.0. I understand that the 1 pH drop should be against the reference sample so i should be aiming for 7.5 during the lighting period.

If anyone has any advice on what may be going on here and how to get best results I'd much appreciate it. At the moment, I've retained the higher bubble rate (2.5 bps and drop checker shows light green) but have gone back to the later CO2 start of 11:00 until I can devise a plan. Ultimately what actually happens in the tank is the most important - i just wanted to see how much I was away from the 1 pH drop that seems typically cited as a target - and ensure I'm getting best value from my CO2 system. Fish (neons, platys, gouramis, red phantoms plus shrimp) are all fine. Ammonia, nitrates and nitrates consistently minimal/zero.

Picture of tank also provided for info.

 

[TrevC]

Other relevant info - in April GH was 23 and KH 13

 

[bazz]

Other relevant info - in April GH was 23 and KH 13

Hi,
Something is not quite making sense to me, I don't know how you can have PH7 tap water with KH13 (assuming the above parameters are the result of testing your tap water) coupled to the fact that your degassed water has a PH of 8.5.
I can't see anything in your tank which would raise the PH 1.5 with GH23 and KH13.
To try and answer your a part of your question though, the use of an use airstone or surface skimmer (I use one of those that is attached to the filter inlet which also keeps the surface clean) will assist in degassing overnight and give you a more stable CO2 environment during the day.
I'm sure someone will come along with an answer with more clarity before long.
Cheers!

 

[dw1305]

Hi all,

Really confusing was that my reference sample (removed from tank and let stand for 24 hrs) showed a pH of 8.5. I had to use a regular ph test because this was outside the scale of the narrow range test. Tap water tested at 7.0. I understand that the 1 pH drop should be against the reference sample so i should be aiming for 7.5 during the lighting period.

Other relevant info - in April GH was 23 and KH 13

Because you live in Cambridgeshire your tap water is going to have dGH (General hardness) and dKH (Carbonate hardness, measured as alkalinity) <"values of ~17 dGH & 17 dKH"> and the pH will be ~ pH 8. <"This thread"> gives the derivation of dGH & dKH and also explains why their ratio is 1 : 1, when they are both derived from limestone (CaCO3) and are present as Ca++ and 2HCO3- ions.

In terms of pH I'd start from the degassed water = pH8 premise, I haven't got a crystal ball, it just relates to the <"geology of the aquifer"> and the level of atmospheric CO2. These <"figures will be very similar"> for most of us in the SE corner of the UK. In terms of the pH reduction with added CO2 have a look at the <"Bouncy Castle"> analogy.

The limestone aquifers in the UK are mainly different and most of them are pure limestone (CaCO3), this is because they were laid down as huge layers of CaCO3 in a deep ocean basin, and have subsequently been compressed deep in the earth, squeezing all of the water (and magnesium ions) out of the limestone.

If you have chalk (above) or Jurassic age limestone aquifers they contain very little magnesium

cheers Darrel

 

[TrevC]

In terms of pH I'd start from the degassed water = pH8 premise, I haven't got a crystal ball, it just relates to the <"geology of the aquifer"> and the level of atmospheric CO2. These <"figures will be very similar"> for most of us in the SE corner of the UK. In terms of the pH reduction with added CO2 have a look at the <"Bouncy Castle"> analogy.

Thx. So i should assume reference pH is 8 so a target pH should be 6.8-7.0 - which is a bit higher than the level I got in the chart I showed - so reduce bps slightly. I should aim reach this target at the lights on point and steady until lights/CO2 off. Following the bouncy castle analogy, it isnt clear to me if mine has many holes in it so I may need to adjust flow so that by early morning pH is back to at least 7.5. I have added the skimmer in my filter inlet and might look for some additional aeration. ( Currently my spray bar has one half pointed slightly down and one half coming in horizontally at the surface - this config has the effect of driving circular motion to get CO2 circulated (and also keeping my floating plants moving).

 

[dw1305]

Hi all,

Thx. So i should assume reference pH is 8 so a target pH should be 6.8-7.0 - which is a bit higher than the level I got in the chart I showed - so reduce bps slightly. I should aim reach this target at the lights on point and steady until lights/CO2 off. Following the bouncy castle analogy.......

That sounds a plan.
I'm <"not a CO2 user">, but if I was? <"I would use drop checker">, purely because it removes a lot of guesswork.

Cheers Darrel