Struggling with plants in my 105 gallon.

[thisguy77724]

So I’m on my second rescape in my 105 gallon tank. I have two other 25 gallon tanks that I have almost zero problems with. My 105g has several different types of plants but non really thrive except for my tiger lotus, jungle val, and some plant I can’t remember the name of. I struggle with bba , and Cyanobacteria constantly! The bba is mostly in the higher flow areas so I’ve recently turned down the flow on my wavemaker to see if that helps. My setup consists of:
-oase biomaster 600
-aquaultra uv sterilizer
-co2 injection using an inline c02 reactor
-Milwaukee co2 controller set to 6.7ph
-1 AI blade set to run 8hrs at 80%, @7k

Substrate consists of pond soil 3” in the back, topped with 1-2” of fine sand, high in the back low in the front.

I fertilize 1 to 2 times a week with Easy green, and easy potassium. I remineralize with Shrimp minerals to kh of 4 and gh of 6. I do 50% water changes every 1 to 2 weeks.

I feel like I’ve tried everything and just can’t seem to get my plants to thrive like in my smaller tank.

I even had some hydrocotyle Japan that is seriously struggling close to the surface, which is weird bc that stuff usually absolutely takes off and grows
Thick for me.

Any suggestions? Pics for reference

 

[Minorhero]

So long and short, you have an imbalance of nutrients vs light. To figure out more we are going to need some info.

Download the photone app for your smart phone, follow the directions on making a diffuser. Take a reading the same distance from your light as your substrate and let us know how much ppfd you are getting.

How long is your light cycle?

Your co2 controller is set to 6.7. But what is your ph of your degassed tap water? Meaning if you take a cup of tap water and let it sit out for 2 days, what is the ph?

What are you nitrates at Midway between water changes, what are they at the water change?

 

[Naturescapes_Rocco]

See this post:

Post in thread 'Cyanobacteria'

Jun 27, 2025

I've been slowly starting a multi-year campaign to get people to understand Cyanobacteria (BGA) better. There's a lot of misinformation in this hobby, but it's 2025, and times are changing. So let's give it a try! There will be a simple summary at the bottom.

Understanding Cyanobacteria (blue-green slime algae, BGA):​

Cyanobacteria are a special "algae" in aquaria because they are actually bacteria. These bacteria can utilize free N2 nitrogen gas from the atmosphere to provide the necessary Nitrogen for growth (source, source). Approx 78% of regular...

• Naturescapes_Rocco

• 
• 

---

Cyano is often (not always, but VERY often) a sign that you don't have nearly enough NO3 in your water column to support healthy plants.

I fertilize 1 to 2 times a week with Easy green, and easy potassium. I remineralize with Shrimp minerals to kh of 4 and gh of 6. I do 50% water changes every 1 to 2 weeks.

How much easy green are you adding to your tank each week? And how much Easy potassium? That is important to know.

 

[thisguy77724]

So long and short, you have an imbalance of nutrients vs light. To figure out more we are going to need some info.

Download the photone app for your smart phone, follow the directions on making a diffuser. Take a reading the same distance from your light as your substrate and let us know how much ppfd you are getting.

How long is your light cycle?

Your co2 controller is set to 6.7. But what is your ph of your degassed tap water? Meaning if you take a cup of tap water and let it sit out for 2 days, what is the ph?

What are you nitrates at Midway between water changes, what are they at the water change?

I’ll download that app and get you those readings once I get off work today.

My light cycle is set to 8hrs.

I use RO/DI water, and I just measured the ph in my barrel and it’s at 7.2.

I’m not sure of the nitrate readings honestly, but I can test my water tonight and let you know. I can do a water change this Friday and let you know what the water parameters are after that too.

 

[Minorhero]

I’ll download that app and get you those readings once I get off work today.

My light cycle is set to 8hrs.

I use RO/DI water, and I just measured the ph in my barrel and it’s at 7.2.

I’m not sure of the nitrate readings honestly, but I can test my water tonight and let you know. I can do a water change this Friday and let you know what the water parameters are after that too.

Is the water in your barrel remineralized? If so, this could be part of the issue depending on light settings. A .5 ph drop might not be enough if you are blasting high light into the tank. The BBA would support that idea.

 

[thisguy77724]

See this post:

Post in thread 'Cyanobacteria'

Jun 27, 2025

I've been slowly starting a multi-year campaign to get people to understand Cyanobacteria (BGA) better. There's a lot of misinformation in this hobby, but it's 2025, and times are changing. So let's give it a try! There will be a simple summary at the bottom.

Understanding Cyanobacteria (blue-green slime algae, BGA):​

Cyanobacteria are a special "algae" in aquaria because they are actually bacteria. These bacteria can utilize free N2 nitrogen gas from the atmosphere to provide the necessary Nitrogen for growth (source, source). Approx 78% of regular...

• Naturescapes_Rocco

• 
• 

---

Cyano is often (not always, but VERY often) a sign that you don't have nearly enough NO3 in your water column to support healthy plants.

How much easy green are you adding to your tank each week? And how much Easy potassium? That is important to know.

I add 10 squirts (recommended dose of one squirt per 10 gallons)of easy green and easy potassium 1 to 2 times each week.

 

[Naturescapes_Rocco]

For Easy Green, Aquarium Co-Op says each pump adds 3 ppm NO3, 0.162 ppm PO4, and 2.01 ppm K at the standard rate of 1 pump per 10 gallons. In your 105 gallon tank, 10 squirts would add about:

• NO3: 2.86 ppm
• PO4: 0.154 ppm
• K: 1.91 ppm

That is super lean. My tanks would get immediate algae if I dosed that much per week. I'd recommend at least doubling or even quadrupling your dose after your weekly 50% WC to help prevent algae, especially cyanobacteria.

For reference, I dose between 20-30ppm NO3, 5-10ppm PO4, and 30-40ppm K every week. I do run larger WC % (66-75%) but even if I did 50% water changes, I'd still be dosing at least 15ppm NO3 minimum.

 

[Pepere]

Each ml of Easy Green added to 10 gallons of water doses the above concentration of nutrients.

Each ml of Easy Potassium added to 10 gallons of water adds 2 ppm.



I would agree at 2 mls per 10 gallons after water change and another ml per 10 gallons midweek for a low to moderately lit tank with no co2.

On a 105 gallon tank premixed liquid ferts get pricey. You are in essence paying to ship a lot of water weight…

There are lower cost options that can be considered

 

[thisguy77724]

For Easy Green, Aquarium Co-Op says each pump adds 3 ppm NO3, 0.162 ppm PO4, and 2.01 ppm K at the standard rate of 1 pump per 10 gallons. In your 105 gallon tank, 10 squirts would add about:

• NO3: 2.86 ppm
• PO4: 0.154 ppm
• K: 1.91 ppm

That is super lean. My tanks would get immediate algae if I dosed that much per week. I'd recommend at least doubling or even quadrupling your dose after your weekly 50% WC to help prevent algae, especially cyanobacteria.

For reference, I dose between 20-30ppm NO3, 5-10ppm PO4, and 30-40ppm K every week. I do run larger WC % (66-75%) but even if I did 50% water changes, I'd still be dosing at least 15ppm NO3 minimum.

 

[thisguy77724]

So isn’t the goal to keep about 30-40ppm of nitrate in the water at all times?

 

[thisguy77724]

Is the water in your barrel remineralized? If so, this could be part of the issue depending on light settings. A .5 ph drop might not be enough if you are blasting high light into the tank. The BBA would support that idea.

No, but I remineralize to a kh of 4 and a gh of 6 after my water changes.

 

[Minorhero]

No, but I remineralize to a kh of 4 and a gh of 6 after my water changes.

Take a clean cup, take some of your tank water and let it degas for 2 days and take a ph reading. Without doing that we can't really be sure how much CO2 you are actually adding. It's possible it's even less than a .5 ph drop.

 

[thisguy77724]

Ok so currently my Nitrates are at 68.5ppm. I believe it’s been about two weeks since my last water change too, so with Nitrates that high I’m guessing I need to get those back down
To around 40?

 

[Koan]

Without doing that we can't really be sure how much CO2 you are actually adding. It's possible it's even less than a .5 ph drop

Another way to dial in your CO2 is to use a CO2 test kit :

Resource Thread 'Hanna CO2 Test Kit: My experience so far (and why you're probably not starting CO2 injection early enough)!'

Mar 27, 2025

The 2hrAquarist legend Dennis Wong tested the Hanna Test Kit vs a $3,000+ CO2 testing device and found accurate results in low kH aquasoil based tanks when compared. $30 for CO2 readings vs $3,000+!

It's a simple kit that comes with simple instructions, two differently sized vials for different detection ranges, a titration syringe phenolphthalein indicator, and an NaOH solution of some unknown concentration to titrate with.

For the range of detection on the Hanna CO2 test kit we want (0-50ppm):

• Add 10mL of aquarium water to the small flask. Add 1...

• Naturescapes_Rocco
• co2 co2 measurement hanna injection test kit titration
• Replies: 40
• Forum: Fertilizing and Aquarium Chemistry

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• 

Since your fertilizer is accumulating to 68ppm, your plants are clearly not eating it. They're not growing fast enough

That is another indicator you may not have anywhere near as much CO2 as you think you do in there, which looks like it may be your limiting factor.

Also you mentioned you're using a wave maker. Is it positioned so that all of your plants are gently moving? Do you have any big dead spots? Your CO2 has to actually get pushed around to each of your plants

I’m guessing I need to get those back down
To around 40

It's not a target number you're looking for, exactly. The numbers are to give an idea how your plants are doing with your current fertilization strategy.

Based on what you have described so far, stabilizing your CO2 and your flow to distribute that CO2 looks like your next step.

@Dennis Wong has a good discussion of that here:

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

Nutrient Tunnel Vision

Is my aquatic plant suffering from a nutrient deficiency? How do I diagnose nutrient deficiency issues? Are there other factors that affect plant growth besides nutrients? This page aims to explain how many factors besides nutrients can affect aquatic plant health.

www.2hraquarist.com

On a 105 gallon tank premixed liquid ferts get pricey. You are in essence paying to ship a lot of water weight

Our own @Burr740 also makes dry fertilizer premixes for macros and micros you add them to a gallon each of distilled water. A lot of us here use his ferts

BurrAqua Post in thread '**Plants In Stock @ BurrAqua.com** - Complete Plant List - Updated In Real Time!'

Apr 30, 2025

Can you put information about your dry salts here too? I’m out of MgSO4, partway through everything else, so trying to figure out the best way to switch over.

Thanks for asking about this. Ive been waiting to list the ferts until retail packaging is ready to roll, that should be done in a couple of weeks. I dont have individual salts, like the MgSO4 you mentioned

What I have is the popular pre-mixed packs of both micros and macros to make your own solution. You just add the entire pack to your dosing container and mix using distilled or RO water

Spoiler: Read More

The micros has Fe DTPA+ Fe...

• Burr740

• 

 

[Minorhero]

Ok so currently my Nitrates are at 68.5ppm. I believe it’s been about two weeks since my last water change too, so with Nitrates that high I’m guessing I need to get those back down
To around 40?

I suspect there are a couple of things going on here that are imbalancing your tank. Definitely take some water before the water change and let it degas. This will be telling.

My current theory is that you are not actually adding much co2 due to the use of the ph controller and your ph is close to your set rate. Additionally, I suspect you have enough mulm/left over fertilizer from your less then weekly water changes to grow some algae.

You also are only using a Oase 600 which has a flow rate of 350 gallons per hour. BUT since that rating is made with the filter empty of media and with no head pressure, the actual flow rate is closer to 175 gallons per hour. Or less then 2 times tank volume turnover per hour. That's really low which is likely helping the Cyno along.

I also suspect that you are pumping high light into this tank, possibly over 100 ppfd at substrate.

All of these taken together is creating the present situation. A lot of this is based on wild speculation though on my part, so we need some more data before we can be sure

 

[JayP]

You also are only using a Oase 600 which has a flow rate of 350 gallons per hour. BUT since that rating is made with the filter empty of media and with no head pressure, the actual flow rate is closer to 175 gallons per hour. Or less then 2 times tank volume turnover per hour. That's really low which is likely helping the Cyno along.

This was one of my first concerns when reading this. The 600 is really underpowered for that size tank as we were just discussing in The Great Big Filter Thread. Even an 850 would be a bit undersized. Filtration wise it may be fine, but good flow moving CO2 and nutrients around would be the concern. I haven't used a wavemaker so I'm not sure how that would play into it.

 

[thisguy77724]

Man you guys have been super informative so far, much appreciated! I’ll report back in two days what the off gassed water’s ph is.

Aside from that, where would you recommend I start? I feel like I’ve got a lot of suggestions and not sure where to start lol.