BGA with a twist

[seangee]

My office tank has persistent recurring cyanobacteria. Its not bad or out of control but I need to siphon it out perhaps every 4-6 weeks and when I do so I also dip my water sprite in H2O2. I have also previously tried a blackout, which worked but it still came back. I suspect the main reason its not out of control is that the tank is fairly acidic (pH < 6). This week I added some alder cones to further reduce the pH but that will take a while to see if it has the desired affect.

Other figures are:
NH4 = NO2 = NO3 = 0, and that's before a water change.
KH=GH =0

I use RO so I am not buying tests for K, PO or Fe and I do 75% water changes weekly so I would be surprised if any of these could build up in sufficient quantities to be a factor.

Internet search did show proper scientific evidence that reducing pH should help but I also found some forum posts (other forums ) that are contradictory. One claimed that raising the pH would help - but I am ignoring that one.

But I did find several posts that suggested increasing the lighting (along with an equal number suggesting reducing it).
One fairly common theme was that BGA thrives in nitrogen deficient conditions and suggest using a fertiliser containing nitrates to try to raise the nitrates to 5ppm. So

1. Should I try increasing my lighting
2. Should I switch fertilisers from TNC lite to TNC complete (or I suppose I could add tap water at a ratio of 1:9 as that has 50 ppm nitrates)
3. should I do both
4. or should I do nothing?

Please don't add to my confusion by guessing , but if you do have any insight I'd love to hear it.

 

[mbsqw1d]

Which plants are in this one sorry Sean?
What's the flow like? And what fish foods are you using? How often do you feed?

 

[Wills]

I learned recently that BGA starts to grow in the substrate particularly around the glass so it is sometimes a good idea to get the scraper between the glass and the substrate. Some people use old store or credit cards and syphon out as they pull it out. If I mention anything else I would just be guessing though.

 

[Colin_T]

The pH has nothing to do with Cyanobacteria (bga) because it grows in fresh and salt water. Sea water has a pH of 8.5, and I have found bga in fresh water streams in the south west of WA and the pH was less than 5.0.

BGA loves nutrients and thrives in water ways with high nutrient levels. Phosphates and nitrates are common causes of BGA outbreaks in natural waterways around here.

Low oxygen levels and low water movement encourage bga but it will also grow in oxygen rich water that has good water movement. However, it is less common in oxygen rich water and fast flowing water.

Red light encourages bga. If you use fluorescent globes and they are more than 12 months old, change the globes and get tubes with a 6500K rating. The higher Kelvin (K) rating has more blue light and a balance of different light wavelengths helps to reduce bga outbreaks.

Uneaten food and excessive use of dry fish foods encourages bga.

 

[seangee]

This is the tank. Mix of dry and live food - just had 2 weeks off food. Apart from when I am away it gets a 75% weekly change with pure RO.

Fairly high flow at the surface and well aerated. It originally started when the tank was new and I had different lights (very old LEDs). I replaced these and it immediately slowed down. What you can see on the substrate grows and spreads incredibly slowly and there is more in the water sprite. Every time I think I am rid of it it re-appears after 4-6 weeks. The 2 sponge filters are powered by electric pumps and the spray bar runs across the entire length. The lights are dimmed but there is enough that the underside of the ludwigia leaves are red. I don't add iron but they do get flourish tabs.

 

[seangee]

Forgot to mention TNC light fertiliser at 0.5ml per day, except when I forget . Recommended dose is 5ml per week. Reduced it to daily in one of the earlier attempts to overcome cyano. Didn't make any difference but the plants seemed healthier that way so I have stuck with it.

 

[mbsqw1d]

I've done some reading, and the Redfield Ratio seems to be pertinent. This is a ratio of carbon: nitrogen: phosphate (106:16:1) that is required for maintaining stability of phytoplankton within both marine and freshwater environments.
It seems that bacterioplankton (cyano), is better (than phytoplankton) at adapting when the Redfield ratio is out of whack. So this is where cyano can survive low nitrogen and high phosphate. cyano would appear more of a yellow-brown than blue-green if its nitrogen deficient.
So if the environment is lacking phytoplankton due to messed up Redfield Ratio, then I would guess that theres a lack of allelochemicals interacting in the environment and keeping bacterioplankton in check.

I found this pdf, amongst many, quite interesting. Btw, Chrome doesn't seem to trust it

https://moritz.botany.ut.ee/~olli/eutrsem/Noges08.pdf

 

[StevenF]

NH4 = NO2 = NO3 = 0, and that's before a water change.
KH=GH =0

Plants need nitrogen to grow. With HN4, NO2 and NO3 all at zero you are deficient in nitrogen and essential plant nutrient. I Keep NO3 between 5 and 10ppm in my RO water tank.

With KH and GH at zero you are likely deficient in calcium and possibly deficient inagnesium. Most fertilizers don't have calcium an essential plant nutrient. Many fertilizers do list magnesium but many treat it as a micronutrient or trace nutrient. It is actually a macro nutrient . When using RO water you need to use a GH booster to insure you have enough calcium and magnesium.

Note if a essential plant nutrient is missing plants will not grow or grow very slow.y. Algae has the same nutrient needs but it needs a lot less and as a result Algae can always do well in a tank that doesn't have enough nutrients for normal plants to grow.

I have no experience with TNC fertilizer but a quickcheck on the web shows the it doesn't have calcium. In my experience when you have multiple nutrients at or near zero changing lighting has little to no effect on the problem.

since you are buying test kits be advised that you want about 1ppm of PO4 which is also an essential plant nutrient. Fe is also an essential plant nutrient and in general you want a level of about 0.1ppm of iron.typically most fertilizer have more than enough iron and potassium. So I would not expect you to be deficient in these.However I have observed in the past that if you have a nitrogen deficiency PO4 levels could be high simply because your plants are not able to use them due to the lake of nitrogen. That could also happen for K and Fe.

 

[mbsqw1d]

since you are buying test kits

I don't think OP is getting test kits because they are using RO water, and with weekly w/c's he wouldn't expect to see a peak in PO4 unless he was massively overfeeding. Pretty sure it's down to Redfield Ratio being out, the system needs more nitrogen. Dunno whether or not TNC will address this or not? Probably going to be trial and error. Adding more of his nitrate heavy tapwater could help?

 

[Colin_T]

Forgot to mention TNC light fertiliser at 0.5ml per day, except when I forget . Recommended dose is 5ml per week. Reduced it to daily in one of the earlier attempts to overcome cyano. Didn't make any difference but the plants seemed healthier that way so I have stuck with it.

That is because plants do better with a steady supply of food rather than a lot of food once a week. If they get food once a week, they suck it all up in a few days and have nothing for the rest of the week. If they get a small amount each day, they get a steady supply each day and do better.

------------------
Cyanobacter bacteria (blue green algae, aka bga) is not actually a plant. It's a photosynthetic bacteria, basically a bacteria that can photosynthesise like a plant does. This means it doesn't need the same nutrients as plants and it can grow anywhere including dark environments. Plant fertilisers or an imbalance of plant fertiliser are unlikely to cause this problem.

 

[Naughts]

I had Cyano and my water is the opposite of yours. I have pH 7.8 and struggle to keep nitrates below 20. I think increasing your nitrates could make it worse.
The trigger for Cyano coincided with extra light in the spring so I moved the tank, but I also had it in the other display tank first so it could have just been cross contamination.
I spent weeks taking out rocks and wood to scrub them and used a soft toothbrush between the glass and the sand. Extra flow made no difference but I stopped using liquid fertiliser because it was accelerating the cyano growth. Eventually the tide turned and it has been eradicated from both tanks.
My conclusion is that it had just run it's course. This is because tank A got it, then tank B, it started receeding in tank A followed by tank B and it was cured in tank A, then tank B. At each stage tank B was about a month behind tank A. It lasted about 3 months.
Sorry you are dealing with this, it took the joy out of the hobby for me for a while. But "this too shall pass" so I vote 'do nothing' if you want to keep the plants happy.
Others may choose to stop ferts until it has gone but I appreciate this is simplifying the ferts issue. It would be better to pin down the ferts imbalance but that is beyond me.

 

[seangee]

That's the frustrating part. Its not bad and its not growing fast - but while it exists it seems to survive everything I tried. Even if I remove all I can see it eventually comes back. I'm pretty sure if I can kill it (all of it) it won't come back. I have 2 other tanks with identical treatment and these are both fine. So is there a way I can create an environment where BGA will actually die while plants continue to thrive.

• Tried increasing GH and KH to the levels I have in my shrimp tank (6 dGH, 3 dKH, pH 7) made no difference
• Brighter lighting, dimmer lighting, shorter light period all made no difference
• Daily water changes and vacs (also removed and washed all plants in H2O2 soln) and it still came back
• Total blackout and zero ferts. It came back
• Stopped ferts altogether. It did work but the plants did not like it either.

Plants and fish all seem to be thriving. I don't want to mess with that and I don't want to do a full tear down so for now it sounds like do nothing is the only real choice and hope @Naughts is correct.

 

[Colin_T]

So is there a way I can create an environment where BGA will actually die while plants continue to thrive.

no.

If it's persistent and won't go, then you can try flushing out the tank and washing everything before setting it back up.

 

[mbsqw1d]

Redfield ratio: C:N:'P) ... cyano is the most flexible at thriving under extreme ratios (where there's 0N for example). Given why cyano was the dominant phytoplankton billions of years ago and ended up terraforming the planet.

Allelopathic balance between phytoplankton, bacterioplankton and macrophytes.
Once cyano has the upper hand, and conditions are such (inbalance of Redfield Ratio) that algae-phytoplankon does not grow, cyano will prevail due to non-competing allelochemicals.