Help Hard time getting rid of gda, diatoms

[Jarno]

Hello everybody im opening this topic since i cant get rid of the algae and im getting a little tired of it

I have a Juwel Rio 350 liter
3x onex daytime 2x colour 1x plant
At 100% 186 par at the bottom (tank is 66cm high)
I have a 1.5 hour build up and 1.5 hour build off 5 hours full light (90% atm because of the algae)
I moved the timing a little earlier yesterday since i tought it may be on to late (22:00) and not getting enough fully darkness for the plants to recover so it goes out now at 20:00

My co2 goes on 2.5 hour before lights go on and half an hour before lights go out
Ph drop of 1.4-1.5 (dropchecker 30mg/l limegreen/yellow)

Filtration: tetra ex 1500, oase biomaster 750 thermo (both with a spraybar creating a roll over), eheim skim 350 and a marine 6000 wavemaker that goes on every hour for 5 minutes (from 12:00-20:00) to distribute loose dirt so the filters will suck it up and keep the plants more clean

Waterchange 50% a week on monday with only RO. Apt sky to a gh of 8

For fertz i use Apt E dosing 6ml a day (keeping the no3 stable trough the whole week from the strategy of Dennis)
I have tried higher dosing aiming at 20mg/l no3 to now leaner dosing.

My plants are not super healthy. The fast growing stems have healthy tops but bad old growth. Even when replanting the healthy parts they turn out the same way.

They are also not as deep red as they should be with 186 par and look like they lack light in the bottom of the tank. My theory is that the 66cm depth is filtering a lot of the spectrum especially red.

The soil is now 3 months in the tank and is 4 months matured if you include priming the soil in a big bucket for bacteries (darkstart)

I had algae before the soil change and still have it now. I tought the soil would be the cause.

I dont know what else i should try or what could be the problem

Thanks in advance for your help and reading this big text

 

[Naturescapes_Rocco 6]

I think your plants are generally starving. The fast growers might have OK new growth from what is left in the soil, but if this is all you're dosing per day then this isn't a lot of food for a tank as densely planted as yours:



I run nutrient levels 15-30x what you're dosing!

 

[Unexpected 4]

Agree with @Naturescapes_Rocco classic not enough food and lowers being consumed. GDA, IMO is an immature tank bacteria wise and lack of healthy robust plant mass. It's not a symptom of too much of anything, it's a lack of something or just plain old too much light with the factors I mentioned present already.

 

[Jarno]

Ive had it running on 80ml a week and got the same result.
Bad old growth and good new growth.
38 ml after waterchange and 6 ml daily as the no3 uptake was 6ml a day. This to not reset the plants every time.
Dennis told me to try getting leaner to starve the gda but keep enough for the plants since higher dosing would not help. So right now i run only on the 6ml upkeep a day and 6ml after change.

What would you guys advise to aim at?

 

[Unexpected 4]

Ive had it running on 80ml a week and got the same result.
Bad old growth and good new growth.
38 ml after waterchange and 6 ml daily as the no3 uptake was 6ml a day. This to not reset the plants every time.
Dennis told me to try getting leaner to starve the gda but keep enough for the plants since higher dosing would not help. So right now i run only on the 6ml upkeep a day and 6ml after change.

What would you guys advise to aim at?

Try to report numbers in ppm if possible, kind of the Universal language so to speak. But, if you are convinced you have enough, then the logical next steps is to double check CO2 and look at your maintenance. I'd go ahead and remove all algae infected leaves or top plants while keeping up on general maintenance. 186 PAR is more than enough, could even be too much for the age of the substrate. Newer subs are not as biologically mature vs say 8 months. All these are factors and will need to be eliminated as possible cause. I will say, and this is my opinion, high PAR can cause more issues than it's worth.

 

[Jarno]

Must say havent tried to measure in tds before to keep an eye on the fertz. Will try that. Very good idea!!
That way i will not only measure and aim the no3 but also all the other elements.
What would you advise for the rising no3 if i need to add more fertz then 6ml

Co2 is enough my water degassed is 6.7
In the pictures you can see my co2 level at the moment.

I will remove algae infected leaves again when i see some positive results in the way of the fertz. All i have done now is replant, trim off algae infested leaves for months just so that new ones can grow Infected. And i dont have motivation anymore.
Here in Holland we have a saying: Mopping the floor while the tap is running.
You can probably guess the meaning

 

[Unexpected 4]

If this was my tank...

I'd cut PAR down by half, raise my dosing to keep NO3 at 30ppm, PO4 around 8ppm and K around 40ppm. I would keep micros around .45ppm Fe weekly dose as a proxy. Keep up on maintenance and make sure CO2 is around 50ppm. Then I would wait because a new substrate doesn't hit its prime for about 6 to 8 months. That said, I use an inert substrate and I just haven't experienced lower PAR reducing colors or negatively affecting plant growth.

My experience with GDA is as follows. New tank, way too much PAR, low nutrients, low plant mass and or a big substrate disturbance.

 

[Jarno]

I personally think new substrates can have these par values even higher or double. Im just to dumb to find the right balance. I have been using massive amounts of fertilizer trying to rule out plants starving. Since algae is often faster there when plants are not growing right then when you add to much nutrients. I have been trying from 50mg/l no3 fosfates 3 fe 1.5 to this almost zero dosing. Im not saying that 6ml i dose now is good. You guys probably are right on the starving part since 6ml is not much at all. Im just trying everything out to see what works for this tank. But everything i do i keep having the same end result.
The plants was like this before the soil change so im not so focused on the substrate. The substrate should even be of higher value to eliminate the algae since its cleaner and richer of nutrients helping the plants to grow better. I do agree new soils arent as stable as a few months old since of the ammonia spikes etc.

 

[Unexpected 4]

Sorry man, but it seems your mind is set on what the solution is. I'm not sure anyone here can ever help you.

 

[Jarno]

So if par was a problem how can a lot of aquascapers like dennis wong for example having 200-300 par in a fresh tank new soil have a algae free tank?
Im not saying i know everything i just know its possible and i wanna find my possible.

 

[Unexpected 4]

So if par was a problem how can a lot of aquascapers like dennis wong for example having 200-300 par in a fresh tank new soil have a algae free tank?
Im not saying i know everything i just know its possible and i wanna find my possible.

Ask him, but I suspect it's the cycling process and the maintenance and a clear understanding of ppm and much more. @Dennis Wong

 

[Koan 31]

All i have done now is replant, trim off algae infested leaves for months just so that new ones can grow Infected. And i dont have motivation anymore.
Here in Holland we have a saying: Mopping the floor while the tap is running.
You can probably guess the meaning

As a rule, hungry plants are unhealthy plants

If your new growth starts out good and then becomes unhealthy, it makes me wonder how much time you are leaving between each change?

Making a change like raising the fertilizer, changing the co2, changing the light.. For any alteration in one of these variables you want to wait four to six weeks for everything to stabilize in your tank before you'll know if it's helping

New Tank Journey | Ugly Duckling

Above- newly planted Lysimachia parvifolia | Samolus parviflorus red showing all the classic signs of adaptation stress- observe the algae-infested leaves. Did we do anything wrong? What must we do now? These are common questions. In the classic children's story, The Ugly Duckling, a young...

www.2hraquarist.com

 

[Kwyet 445]

So if par was a problem how can a lot of aquascapers like dennis wong for example having 200-300 par in a fresh tank new soil have a algae free tank?
Im not saying i know everything i just know its possible and i wanna find my possible.

This might help:

Thread 'Speed running setups. Settling in a planted tank fast.'

Jun 16, 2025

In last couple of years I was testing aquasoil compositions (amongst other things) and wanted to grow in tanks as quickly as possible. This is the method I used which could be helpful for folks starting new tanks or for folks wanting to solve problems (principally algae as its the main thing that hits new tanks) quickly. Its an approach that can work for folks with more time on their hands and wonder if they can "massage" out results more quickly.

These are the tanks that I grew in less than 8 weeks, with the fastest being just 4 weeks. These tanks have multiple usages - product testing...

• Dennis Wong
• Replies: 10
• Forum: Planted Aquarium Discussion

• 
• 

 

[Dennis Wong 2]

I think your plants are generally starving. The fast growers might have OK new growth from what is left in the soil, but if this is all you're dosing per day then this isn't a lot of food for a tank as densely planted as yours:

View attachment 18323

I run nutrient levels 15-30x what you're dosing!

I'm not sure how where the calculator gets its figures, but its off by about 50% for the total nitrogen.

On a side note, I've seen Jarno's tank over a long time by now, when he used to run more heavy nutrient levels less. It never worked for his tank. What is interesting is if you look at his plant growth, its not due to a lack of nutrients at all. I shall not go over the very long discourse that I already have with him to no avail - he can copy/paste my comments over the past years? with him if he wants

I feel that there is something else off about his system at a fundamental level, nothing simple, because he has played with all the parameters, replanting etc. The plants always reach a point where they just seem to crash, even for easy stuff.

The daily dosing is the similar level I use for this tank (ranges from 5 to 7ml, depending on fish feeding )- which adds around 2ppm upkeep daily for nitrate equivalent:
The difference is that I maintain a saturation rate of around 15-20ppm by redosing 20-25 ml after water changes, which I think he does also. This is not a fresh aquasoil tank - soil is 2 years old, but I add 1% new aquasoil by weight per month. All described here:

4ft Rotala florida community aquarium: Showcasing the 2hr Way

Full details of tank parameters, plants and fish species, and the maintenance regime of the 4ft Rotala florida aquascape are described here.

www.2hraquarist.com

 

[Naturescapes_Rocco 6]

That's a tough one, then. Levels are still much lower than I'd attempt for that much light, but maybe it's a microbiological issue. Could also be CO2 stability over the photoperiod. Either way, somethings definitely off and I know how frustrating that can be @Jarno !

 

[Jarno]

That's a tough one, then. Levels are still much lower than I'd attempt for that much light, but maybe it's a microbiological issue. Could also be CO2 stability over the photoperiod. Either way, somethings definitely off and I know how frustrating that can be @Jarno !

Yes they are, the nutrient levels are the lowest i have ever done.
But at some point you just dont know what to do anymore. So instead of the normal cause of algae "to less fertz". I tried starving the algae by only adding my daily upkeep for the plants

This was a test of co2 when i had my lights on at 14:00. 15:30 lights was at 100%
12:00 co2 start
13:13 5.7
14:15 5.5
16:00 5.4
17:20 5.34
17:40 5.3
18:10 5.29
18:40 5.25
19:30 5.23

 

[Dennis Wong 2]

That's a tough one, then. Levels are still much lower than I'd attempt for that much light, but maybe it's a microbiological issue. Could also be CO2 stability over the photoperiod. Either way, somethings definitely off and I know how frustrating that can be @Jarno !

I find that the idea that higher light means higher nutrient levels is required, is really a nutrient tunnel vision comment. Ultimately what determines algae-resistance is healthy plants - but you do not need higher nutrient levels simply because there is more light. Whether or not to have higher nutrient levels depends on the plant mix used - i.e. are they species that do better with heavier water column dosing? Like Tonina species for example.

You can run near 0 NO3 levels, for example, and grow slow growers in high light perfectly fine - if the species tolerate leaner water column dosing/or are balanced with richer substrate. dosing rate = uptake rate with little residue works well for a lot of species. If plants can grow healthy at lean levels, that's all that matters. You do not need high water column saturation rates just because high light is used. Higher water column saturation should match the species involved.





Its not purely a matter of blasting CO2 either.
Both Sudipta shaw and myself run high light on low tech tanks.




In the case above, Anubias at 160 PAR, low tech tank. Once again, if the species can be healthy in that environment, algae resistance will come in.
Its not about matching CO2 or nutrients to light levels blindly, but according to what species needs. In his tank,

His tank has a lot of growth - if his levels were anywhere near lean, his plants will look very different. True lean levels give smaller top growth as well (like my Meta above), and his are normal/large. He is not growing super CO2 sensitive species like BV/Red Erios. Everything he has grown at probably 15-30ppm range.

Unstable dosing could cause a whole lot of issues - and my comment is that a lot of folks problems are caused by nutrient instability rather than a lack of nutrients per se. I have already told him this, and from what I understand, he has already tried to stabilize the nutrient levels.

 

[Dennis Wong 2]

and a marine 6000 wavemaker that goes on every hour for 5 minutes (from 12:00-20:00) to distribute loose dirt so the filters will suck it up and keep the plants more clean

I just saw this, and I really think you should not do this. Periodical turbulence isn't helpful for planted setups.

 

[Jarno]

I just saw this, and I really think you should not do this. Periodical turbulence isn't helpful for planted setups.

I installed it like this 3-4 days ago
But i will undo it
Even chatgpt is scared of you. He brought me this idea and when i showed him the screenshot he said:

I actually think Dennis Wong's advice carries more weight than mine. He has a tremendous amount of experience with high-end planted aquariums.
His point isn't that more flow is bad, but that periodic on/off turbulence is not ideal.

 

[ScaperHaynes 2]

Thought I'd join this thread, as I've had similar issues with diatoms never seeming to go away. However, a lot of this was probably because I attempted to do DIY fertz and a DIY horizontal reactor on my very first planted aquarium. As someone who had reasonably good success with reef aquariums, I wayyy overestimated my abilities with planted tanks. That resulted in 10 months of hell trying to diagnose the issues and nearly quitting the hobby several times.

Long story short, I'm fairly certain that the most likely causes were #1 Unstable CO2 from my crappy DIY reactor #2 Unstable Nutrients #3 Generally being a noob #4 Not changing my DI resin on time because I thought it wasn't as crucial for freshwater.

I took a break from the hobby by running my tank in "dark start" mode for about 2 months, and I let my plants grow out emersed in some plastic bins to get a larger plant mass without combating algae.

I changed to off the shelf products for CO2 Injection (In-line diffuser) and fertilization (APT 3) so that I could start fresh with less variables to track (just as Dennis suggested in a recent podcast).

A little over a week ago I replanted the tank, performed ~50% water changes daily and things were looking SO much better than before. I thought I'd finally figured things out. But around day 8, the diatoms started to be much more noticable despite my best efforts to manually remove algae with daily water changes in the first week.

Of course I've read Dennis' algae control articles dozens of times but have some trouble with the implementation.

Where I struggle with this, is that by following the advice to trim off the tops and replant, the plant mass in the tank is reduced and the algae seems to gain the advantage.

With the carpeting plants, removing algae manually is pretty much impossible with a brush or by hand without ripping the plant up entirely. I trim away stuff that is clearly dead/melting, but algae seems to cover leaves about the same rate that new ones grow. I'd have to use way too much H2O2 to treat everything.

Either way, I fear that I'm re-living the same cycle where algae isn't on the very newest growth, but takes over anything more than a few days old.

I'm hoping that because my CO2 and nutrients will be more stable using off-the-shelf products that I'll be able to get past this diatom phase this time. I'd expect that if parameters are held stable, new growth won't be taken over by algae within a few days and therefore break the cycle?

I'd love the experts here to take a look at the current tank parameters and tell me if anything looks off or what I should do differently.

Tank: ADA60P
Light: Twinstar S | 95 PAR @ Substrate for 6 hours/day
CO2: UNS In-line Diffuser | 35-40ppm (Tested Hanna CO2 Test Kit) | On 2.5hrs prior to lights, off 30 mins before lights off
Filter: Oase 350 with 30ppi Sponge Only
Soil: Amazonia II Aquasoil (almost 10 months old, no root tabs used but also hasn't ever seen a heavy plant load)
Fertz: APT 3 —> 1 ml/day first week, bumped up to 2ml/day once plants filled out a bit... probably shouldn't have increased this quickly... I used the APT calculator but wasn't sure whether to use the "lightly planted" dose or default dose.
Water: RODI remineralized with 30ppm Ca and 6ppm Mg.
50% water changes daily for first week
Plants: Rotala blood red, crypto wendtii, hydrocotyle tripartita, pearlweed, javafern, hygrophila pinnatifida

Tank is in farm mode so that I can learn to grow plants before introducing wood, stone, etc.

My questions for the experts:

• Is it a problem that plant mass is reduced when you trim off the good parts of the plant to replant and discard the algae covered stuff?
• How do you deal with this with carpeting plants that are much harder to clean off manually and separate new growth from old?
• APT3 is a zero-bound system, which I understand to be used with nutrient rich soil. Is it potentially problematic that I'm using old soil despite it never having seen a full plant load?