CO2 and light levels

[mn_aquascape]

Hello everyone. Back in the game after a lengthy hiatus, and a few failed attempts to get after it again. Kids are older and super into which makes all this super fun again!

I run a 120cm rimless with 2 x Chihiros RGB II pendants. I had the dreaded dim red light all night problem and recently replaced the blue tooth controller and PCB boards on both units to v.10. Chihiros should do better, but thats a totally different post. Tank has been up and running for maybe 2 months now

Substrate: BDBS
Water: RO remineralized with APT Sky to GH 7ish and 0 KH. 90% change weekly.
Fish: booming colony of Sanke Swordtails, some ottos, and a handful of bloody mary shrimps.
Ferts: dry salts to full EI levels using good old CSMB
Filtration: one of those stainless canisters with a DC pump on top. Got it from GLA when they were in that game.
CO2: GLA regulator run through a NilocG reactor. On 2 hours before lights on, off 1 hour before lights out. (Light cycle 7 hours)
Plants: mix of Hygros, Ludwigias and a few other things. I like like to grow basic plants, really well, and dont have the patience for delicate things. I get a little lazy from time to time.

Question: I've been fighting some frustrating stunted and twisted tips on things like Ludwigia inclinata, some really frustrating melting on Heteranthera zosterfolia, some sad drooping leaves on Ludwigia glandulosa, and a touch of greenish water and maybe a touch of GSA/GDA. I'm not an expert, but I'm confidently ruling out nutrient problems given I'm on full EI. Not a micro toxicity, since that horse has been beaten to absolute death and I'm 90% water change weekly.

Im stating to wonder if CO2 isnt right. I guess I don't do the whole pH measurement thing... again, just a little lazy, and I think my plants are telling me what I need to know. I feel like ive maxed out everything I can with CO2, so my brain is starting to think lights are just too much.

This week I dialed the lights back to 70% after my water change on Sunday. I think I'm starting to see some small improvements in the stunted and twisted tips.

Could it be my lights were just too much, driving photosynthesis too fast and depleting CO2 levels during the day resulting in fluctuations the plants didn't appreciate? By turning the lights down to 70% did I take my foot off the accelerator allowing photosynthesis to be better balanced throughout the day with the CO2 being added to the system? I also reduced plant mass a fair amount this past week, which might have also reduced CO2 demand. Is my rationale wrong on this? Is it possible that these stupid high output lights, like Chihiros, when run at 100% are just too much for a CO2 reactor to keep up with in a greedy stem plant tank?

Thanks fellow planted tank nerds. Its good to be back in the game. I'll post some updates on our liverbearer low tech planted tank rack sometime soon too.

Haphazard photo as I walked by the tank tonight, attached for post tax, and yes.... we all see the slightly green/cloudy water.

--Steve

 

[techman81]

Some good information about testing CO2 with the Hanna Co2 Test Kit here:
Hanna CO2 Test Kit

 

[Koan]

stating to wonder if CO2 isnt right. I guess I don't do the whole pH measurement thing

This will help

Journal Post in thread 'Recovering from disaster: My 120P journey.'

Jan 3, 2026

Right now I'm thinking its inconsistency in the CO2 that I'm just not seeing

Using the Hanna CO2 kit, to directly measure CO2 instead of inferring from pH drop, can also remove this uncertainty for you

• Koan

• 

just too much for a CO2 reactor to keep up with in a greedy stem plant tank

Have a look at these

Article 'Yugang CO2 Reactor - A Guide'

Contents: Benefits of Yugang reactor Calculate the reactor dimensions Overflow mode, regulator mode, pH/CO2 controller Overflow mode, step by step instruction Regulator mode, pH/CO2 controller mode, step by...

• Yugang
• Sep 15, 2025
• 20 min read
• Reaction score: 10
• Comments: 10
• Category: CO2 in the Planted Aquarium

Post in thread 'New Yugang Testing'

Dec 3, 2025

I realize that it might be helpful to explain how to actually dial in a CO2 setup!

First, you have to keep as many variables constant as possible. If you are constantly changing these, it makes it VERY hard to dial in CO2 injection:

Things that change CO2 levels in the water are:

• Injection rate (bubbles per second for bubble counters, or SCCM if using flowmeter. Also rotatable/adjustable horizontal reactors)
• Temperature (warmer = less CO2, colder = more CO2)
• Surface agitation (how near your filter/lily pipe is towards the surface of the water)
• Surface scum (more...

• Naturescapes_Rocco

• 
• 

 

[CincyScaper]

Co2 : Agree with the Hanna Co2 kit. The PH meter also helped me, but just needs the degassed baseline. The PH meter is great for a trend.

Lighting: Recommend the Photone app to get the PAR rating. You are obviously at an advanced stage but could read through some of the journals to see what kind of PAR is being used.

 

[Dennis Wong]

For less picky plant species (this includes L. glandulosa and Heteranthera zosterfolia), fluctuations in CO2 levels do not result in twisted leaves or stunted tops- short of severe dips like stopping CO2 entirely. Your strong lighting is also an impact factor you can rule out - its still largely within normal ranges for aquariums in that sense.

What could be a cause, and quite a common one at that, in EL tanks is nutrient level fluctuations especially when rebalancing levels during large water changes.
The idea is explained more in detail with charts below:

Why nutrient level stability matters for planted aquariums

Nutrient stability in planted aquariums - how to have stable nutrient levels and why it is important. Avoid triggering algae and tip stunting.

www.2hraquarist.com

 

[mn_aquascape]

For less picky plant species (this includes L. glandulosa and Heteranthera zosterfolia), fluctuations in CO2 levels do not result in twisted leaves or stunted tops- short of severe dips like stopping CO2 entirely. Your strong lighting is also an impact factor you can rule out - its still largely within normal ranges for aquariums in that sense.

What could be a cause, and quite a common one at that, in EL tanks is nutrient level fluctuations especially when rebalancing levels during large water changes.
The idea is explained more in detail with charts below:

Why nutrient level stability matters for planted aquariums

Nutrient stability in planted aquariums - how to have stable nutrient levels and why it is important. Avoid triggering algae and tip stunting.

www.2hraquarist.com

Thanks Dennis. Appreciate the help.

I do front load the entire weeks worth macros on water change day. Maybe levels are dropping further than I think they are by the end of the week. I guess ill have to grab a NO3 test kit and check a few times throughout the week. Maybe Ill need to add a second dose of macros mid week.

Do you think there would be other signs of nutrient deficiency? Or is the twisted tips enough?

Curious still if reducing light intensity may also help with this? Does reducing lighting reduce nutrient uptake? Things have been looking real good this week so far. Not a speck of GDA on the glass.

--Steve

 

[Dennis Wong]

Thanks Dennis. Appreciate the help.

I do front load the entire weeks worth macros on water change day. Maybe levels are dropping further than I think they are by the end of the week. I guess ill have to grab a NO3 test kit and check a few times throughout the week. Maybe Ill need to add a second dose of macros mid week.

Do you think there would be other signs of nutrient deficiency? Or is the twisted tips enough?

Curious still if reducing light intensity may also help with this? Does reducing lighting reduce nutrient uptake? Things have been looking real good this week so far. Not a speck of GDA on the glass.

--Steve

Might not be deficiency at all, could be just fluctuating levels or excess. Why is the assumption in all plant forums that nutrient deficiency is the default state of plants when something goes wrong ? The weird thing is that this assumption is the strongest among the crowd that uses the heaviest dosing approaches. Quite an interesting observation. It is like going to a gym where everyone is actively exercising, then when someone gets a headache, the others immediate ask - is this due to a lack of exercise ?? The contrary opposite is often more likely - that guy in the gym is probably not suffering from a lack of exercise. Highly likely in such a scenario it is due to over exercise or poor execution of said exercise, or non gym factors.

I think that most tanks with higher uptake rates, such as CO2 injected, higher light, densely planted tanks, will not be stable with once a week dosing. Even if you front load say 30ppm of NO3, and your uptake rate is just 3ppm a day, by end of week you are left with 10ppm of NO3 which spikes back to 30+ppm by next water change? That's quite a big difference in NO3 saturation levels. This itself causes issues.

In a perfect scenarios, daily dosing will exactly hit the uptake rate, regardless of your initial saturation rate. 2 perfect examples below:
Example A: Front load 5ppm NO3 on day 1. Tank uptake rate is 3ppm NO3 a day. NO3 is dosed at 3ppm a day. NO3 stays consistent at 5ppm.
Example B: Front load 30ppm NO3 on day 1. Tank uptake rate is 6ppm NO3 a day. NO3 is dosed at 6ppm a day. NO3 stays consistent at 30ppm.

It could work if your uptake rate is tiny relatively to your initial saturation rate. I.e. front load 40ppm NO3, and say your uptake rate is just 1ppm a day. Your nutrient levels stay within 30-40ppm within the week that is fine. The larger your daily uptake rate vs your initial saturation rate, the worst it gets. High light, dense, CO2 injected tanks tend to have uptake rates, which makes juggling the daily dosing more difficult - and this is the reason why most high tech face occasional plant issues from instability.

Reducing light slows down the whole growth process and can temper poor approaches to nutrient dosing/CO2 etc. However, you get less dense growth and reduced coloration of course.

 

[Naturescapes_Rocco]

If anyone wants to visually experiment with what Dennis is talking about, I made a calculator that helps you see on a graph how stable levels of nutrients are, relative to:

• Dosing frequency
• Dosing amount
• Plant uptake
• Water change %

Nutrient Accumulation Calculator

 

[Koan]

I made a calculator that helps you see on a graph how stable levels of nutrients are, relative to:

• Dosing frequency
• Dosing amount
• Plant uptake
• Water change %

This

 

[plantbrain]

This is for PO4 uptake. At low or limiting levels, a much more efficient uptake transporter is created by the plant that can grab every tiny amount. But this comes with a cost of more energy to do so and if the PO4 increases, then it's much less effective. Plants often have 2-3 types of transporters to optimize their external nutrient environment. Now it takes some time to make such cellular protein machinery. If the ppms are all over the place, this can confuse the plant. The Solution is to maintain a stable ppm, but that's often harder for many people.