High Ph, Low Co2

[pwnell]

I have been keeping marine aquariums for 6 years and have never struggled maintaining all my water parameters at adequate levels.

However, when I recently set up a 14g tropical aquarium, I've met my match it seems. No matter what I do I cannot get my pH and CO2 levels in an acceptable range. An no, I am not chasing pH. My values are off the charts.

Temp: 25C
Alk: 3dKH (I dropped it gradually from 5dKH in the hope this would help)
pH: 7.8
GH: 8dKH

According to this table, my CO2 level is 1.4ppm, but should ideally be 15 - 25ppm. That means a pH of about 6.8 for this alkalinity level. Clearly I am way out.

The tank only has a return pump - no other flow. Surface agitation is very low, just enough to break any films developing on the surface. I have added four plants. One piece of driftwood (which I cooked for 15 minutes before adding it to the tank). The tank has been up for 2 weeks. Only livestock is one male betta.

Any advice? I have read countless articles that you do not need a high tech setup to keep tropical fish. But at this stage it seems like I need to go buy a CO2 reactor, which I really do not want to do.

Oh yes - I am using RO water that I remineralise using Seachem Equilibrium (GH supplement), and add Seachem alkalinity buffer and acid buffer in a 2:1 ratio. I have no choice and cannot use my tap water as is as it has a TDS of 17ppm, Alk = 0dKH and GH = 0dKH.

 

[BerryAttack]

for the CO2 add a bubblier. i'll boost the oxygen levels and keep the water moving more.. and bettas are okay with medium moving water... keeps them fit, but have a place were he can hang out and rest.

for the pH i never have a problem with mine.. sooo i cant help u there.

 

[pwnell]

I am not following you. If I add an airstone or anything that brings air into the water, I will be bringing in 20% O and 0.03% CO2 - this will only raise the pH, it will not lower it. And it will not bring in any significant amount of CO2.

 

[gregswimm]

You really ony need to worry about CO2 in a planted tank with high light. Acording to that chart, you want to be around 6.6ppm. It goes off your KH (alk) not the GH. GH does nothing to buffer an acid and is not measured in dKH but in dGH (degrees of carbonate hardness vs degrees of general hardness).
The only reason I monitor GH in my planted tank is to monitor fertilizer consumption.


How tall is your tank and what light do you have over it?

 

[pwnell]

Thank you for the reply. I have lots of plants and 2 x 24W PC fluorescents... I know the chart works off KH and not GH, I merely listed GH for completeness sake. As I mentioned, I lowered KH to 3dKH. A pH of 7.8 is way too high - it means I only have 1.4ppm CO2 in the water at an alkalinity of 3dKH. So it still leaves the question, how do I raise CO2 and lower pH without having to dose something daily.

 

[gregswimm]

When CO2 gets disolved in water it becomes carbonic acid (H[sub][sup]2[/sup][/sub]CO[sub][sup]3[/sup][/sub]). Carbonic acid will further react with substances in your water and produce hydrogen ions (H[sup]+[/sup]) aka protons. The H[sup]+[/sup] concentration is measured with pH.

Alkalinity aka KH (carbonate hardness), is comprised of carbonate and bicarbonate anions. These anions react with an acid (more accurately the H[sup]+[/sup] given by the acid) and cause it not to change to pH by eliminating all the H[sup]+[/sup]. If you have more acid than the carbonates can react with, then you will see this in a pH change.

General Hardness (GH) is the measure of divalent metal ions (mainly calcium and magnesium) in a solution. This has little to no impact on the ability to neutralize an acid.

 

[gregswimm]

Thank you for the reply. I have lots of plants and 2 x 24W PC fluorescents... I know the chart works off KH and not GH, I merely listed GH for completeness sake. As I mentioned, I lowered KH to 3dKH. A pH of 7.8 is way too high - it means I only have 1.4ppm CO2 in the water at an alkalinity of 3dKH. So it still leaves the question, how do I raise CO2 and lower pH without having to dose something daily.

Measuring and dosing CO2 is unnecessary for the average planted tank. CO2 really only needs to be injected in high light, heavily planted tanks and this comes with the need to dose various ferts in various quantities as well as following a regime such as the estimative index. Another issue is keeping consitent and stable levels of CO2, which is crucial for plant growth and keeping algae at bay.

The best way to inject CO2 is to get a tank of it, either a 50lb tank or a tank for a paintball gun. Buy a regulator (and converter if you are using a paintball tank), a bubble counter, a diffuser and airline that is designed to handle CO2.

Edit: dosing CO2 will lower the pH. You won't be able to raise the CO2 (lower the pH) without adding anything to the tank, unless you change the amount of CO2 that is in the air of the room the tank is in.

 

[pwnell]

Any other ways than CO[sub]2[/sub] injection? I am sure there must be people who uses RO water, remineralise them and have good pH / Alkalinity / CO[sub]2[/sub] levels - not so? What am I missing from my setup?

 

[gregswimm]

You can dose acid to lower the pH but it won't give you any extra CO2. Why do you feel the need to artificially raise your CO2 levels?

 

[pwnell]

I assumed if plants require 15 - 25ppm, and I only have 1ppm, then I am in trouble. Also, acid buffers do not lower my pH. I have lowered my Alkalinity using a metal based acid buffer from 5.5dKH to 3dKH and pH dropped only from 7.9 to 7.8.

 

[gregswimm]

Plants don't require certain levels of CO2. They aren't like corals where you have to have your Alk, Ca, and Mg within ranges for them to grow. Your plants will get enough CO2 from gas excange at the surface. Not like your betas are producing copious amounts of CO2 where you want to limit the agitation to keep the CO2 in the water. If anything surface agitation will bring in more CO2 for your plants and help gas out some of the O2 produced.

The ONLY reason CO2 is dosed in high light tanks is to improve growth rate and get growth rate to the point where the plant is out competing algae for resources. In this situation the plants will consume copious amounts of nutrients so fertilization is a must, or they eliminate whichever nutrient happens to be the limiting factor for their growth (Often Iron, Potassium, Phosphate, and sometimes Nitrate in lightly stocked tanks). It is especially imperative to fertilize with RO water adding your macro nutes (your N-P-K) and micro nutes (Mo, S, Ca, Mg, Zn, Mn, B, Co, Cu). If you have lots of swords/valls I would lump Fe in with the Macros.

15-30 µmol of PAR does not need CO2 injection
35-50 µmol of PAR may need some CO2 to keep away unsightly algae
>50 µmol of PAR needs pressurized CO2 or you are going to be over run with algae.