Backyard Aquaponics
A place to discuss aquaponics

Hi team! I have a slight algae issue in my DWC tanks (something I am new to). Since I put in some wild duckweed (I know rookie,but it's always cleared up before) I seem to have a bit of "string algae", my name for it anyways.

No build up anywhere other then DWC. Which I'm assuming is an issue as its clinging to roots. I've tried scrubbing tanks, and pulling out everyday or two.

So questions, how bad is this for plant growth? Is there any options? A caveat empor is that I plan on cladding these in next week or two, so currently IBC's are in protected. What can I do? Should I put fish/yabbies/prawns in tanks? Some pics to show where I am at. Won't bother saying what they are with picks, TAPATALK seems to move them around... But first one should be area I am talking about, second algae in question, and third algae on roots.

For those of you that don't know my system (how dare you :p), I run a chop2 (don't judge me haha, I have my reasons!), two IBC FT's with Silvers in one (25x10-15cm and 4 x 35cm) and guppies, prawns and yabbies in the other. I have 4 x Gravel 300L GB's, and 4 x 600-700 L DWCS (new addition). PH is at 8.2 (newer system), ammonia at 0.25 (a little spike since new fish came in 10 days ago), nitrites and nitrates at 0. Temp is currently 29 deg c

I don't think you can do much about it without controlling the light getting into it. And I think algae on the roots would block the uptake of the water/nutes (but depends on how much it's over the roots, I've never had to deal with it.

Just curious, how well does the ice cream freezer hold water? Did you need to seal up the edges?

string algae. Unfortunately it is harder to shake than the normal green algae (that is particles making water green). String algae is a bad one for taking oxygen and killing fish.

cannot advise best option when you have fish as my experience is with goldfish - in which case you can use many of the pond products (in such cases I have been willing to accept it may not be organic for the GB).


It is covered on the main BYAP page but limited advice. Mentioned quite a bit on web (Google it)

"Stringy or filamentous algae, not very nice and it can start to take over your fish tank with its long strands of algae. Try to keep the light off the water if you can by covering the tank. Remove what you can from the sides of the tank manually. Perhaps add some known algae eaters to the tank if you can. We added a few yabbies to one of our tanks which had filamentous algae, they have cleaned it up nicely." from BYAP FAQ.

also search it here - there are a few posts on the topic.

Just to add to what Darren said, be careful with the pond algae removers. They'll likely kill all your plants too, depending on the type. I've see a few sad posts on the topic.

p.s. you have basically provided the algae equivalent of bliss......

nutrient rich water + light + opportunity = very productive bad combination.

may be best to isolate it from the rest of system if not too late then basically clean it out completely,
new water and put the rafts back in place.

this stuff is basically the blue-green alage type thing that clogs up ponds/waterways etc.

I'm pretty sure that blue-green algae and filamentous algae are two different things although since they both like the same conditions there is a good bet you often see them together.

Thanks team, much appreciated! My searching skills mustn't be much chop, I did go looking. Yeah I'll keep cleaning, and chuck some yabbies in. Will they eat my roots? My biggest worry is they will climb out of DWC haha.

I think the algae is "in" my system, so don't know about cleaning it out, as the duckweed was put into FT and migrated, so don't think cleaning will help.

Can I lightly "rub" roots to get algae off or is this no good either?

Oh and Colum, I just had to deal around the inside of the freezer where I put SLO pipe work. Uniseal covered the outside. I went with if its food safe, it's AP safe, mind you Bodgy is doing same thing but lining his, so I may need to do some research. Hasn't leaked.... But may be leaching?

"I'm pretty sure that blue-green algae and filamentous algae are two different things although since they both like the same conditions there is a good bet you often see them together."

yep good point Stuart*. I have had both types (not in AP but in water collection sump tank that I grew duck weed in) - though maybe that is simply what filament grows into when it goes berserk??

I suspect that either way irrespective of what is actually is the big sludgy stuff is bad news and unlikely to get managed "within system". The pond type chemicals to take it out start getting pretty serious and not good for a food system - so taking the one DWC out, cleaning and cladding it then filling with new water would hopefully mean that the bits remaining in the system will be dealt with naturally.


* actually my error, in original reply I thought there was another picture showing a white pipe with a filament coming from it but that must have been somewhere else.

I used to have problems with this when my pH was higher. As your pH goes down I suspect this will be less of an issue. I'm not certain the pH was the cure but the algae is no longer a problem and the reduction in pH coincided with it's disappearance. You could give a try at lowering it using some acid and see if that helps but do it gradually 0.4 pH points per day. Everyone's system is a bit different so I can't tell you how much acid it will take (probably not much though).

Hydrochloric acid (HCl)(aka muriatic acid) - Add to topup water - adjust this to 6.0 to 6.5 and let stand 24 hours before adding to system. This will lower the system pH gradually over time.

I've got the same problem in my DWC tank.

Because it took ages to get the rafts a good deal of algae built up within the tank.

My plan is to leave it there because:

Now that the tank is covered in rafts its growth will be drastically reduced.
the snails in there will eat it and while they are eating it they won't be eating the roots of my plants.
removing it from the roots of the plants could cause more damage.
there is plenty of air in the tank so its less likely that the roots will get suffocated.
My experience with algae is that over time it corrects its self.

Yeah same reasoning for me on rafts Stu, except I had mine and was just being lazy (and working I guess).

More air is the Xmas present I am buying myself.