Algae Control

Algae is a constant battle for hydroponic growers.

Normally it is just a visual nuisance but if it is left to colonise the growing system or increase in density it can start to compete with plants for dissolved oxygen and nutrient.

Algae will always thrive if sunlight and an exposed nutrient solution is available.

It won’t grow on a dry surface or on one deprived of sunlight.

Chemical methods will not eliminate algae. All they can do is help to reduce the problem.

You have to be careful that any chemical you use to kill algae does not damage the sensitive roots on your crop. Algae is also plant-life so anything that kills algae also has the potential to harm root systems.

Algae will quickly re-establish itself after any chemical is added to your system to treat it, so you need to be prepared for the increased and ongoing running costs of going down the road of chemical control and the realisation that you can’t eliminate it completely.

Prevention is therefore better than the cure.

  • Turn off the flow to any unused NFT gullies so they sit dry (or flip them upside down).
  • Cover any unused plant holes or insert growpots into the holes to reduce light availability.
  • Grow your seedlings to a later stage before transplanting into the NFT gullies so the leaves cover the plant holes better and reduce light transmission inside the NFT gullies.
  • Cover the tops of rockwool blocks with small squares of panda film (unable to do this on smaller cubes).
  • Cover exposed tanks but still enable good ventilation of the tank (e.g a raised tank lid)
  • The use of  shadecloth can reduce light intensity and algae loading but be careful not to exceed 40% shading or you can stretch (elongate) the crop.
  • Use a 130 micron screen filter on the outgoing flow and a 500 mesh filter bag on the return flow to reduce organic loading in the recirculating solution.
  • Carbon filtration or slow sand filtration on a separate recirculating pump that sucks from and drops straight back into the recirculating tank can help in certain cases. This helps to remove any living or dead algae in suspension within the nutrient solution.
  • Always clean grow pots, benches and NFT gullies after harvest. Don’t be tempted to do another cycle in an unclean gully or else the algae loading will get higher.
  • Dump your tank more regularly so the full body of water is replaced with fresh water and fresh nutrients. This removes any dead and living algae that may be suspended in solution and restores the nutrients back to full balance. NFT tanks should be dumped every 4 – 6 weeks unless a laboratory test says otherwise.
  • Use a Gully Brush or a Hover Blaster gully cleaner for efficient cleaning of NFT gullies.

If all of these measures fail, and the algae is becoming a serious problem, only then should chemical treatment be considered to complement those strategies:

Algae can help to be suppressed by the monthly addition of 3.7grams of Blue Stone (Copper Sulphate) per 1000L into the NFT or recirculating tank system. Add directly to the catchment tank. Do this at least 5 days before a dump. 

Oxine (an Oxidiser) shown on our website, can help to reduce algae at a dose of 2ppm (activated)  but it won’t eliminate it.

Oxine is safer on live roots compared to Hydrogen Peroxide provided you don’t exceed the 2ppm (activated) rates as directed on our website.

Obviously, some crop types are more resilient than others to oxidisers but if you are dealing with crops that have young, sensitive roots (e.g. microgreens) always try in a small test system first.

If you are adding Oxine you need to be 100% sure you know the solution volume in the system you are basing your calculations on so you don’t risk overdosing it. Oxine Test Strips are also available for additional accuracy.  

The best method for using Oxine is to add the activated Oxine to the fresh water holding tank at 2ppm as you know exactly what volume is in that tank (no solution is trapped out in the pipes or gullies etc). Then the Oxine will fully sanitise the contents of fresh water in that tank with 12 hours contact time (e.g no Pythium)  and it will then pass a residual into the main hydroponic system tank via the fill pump and ball cock valve.

Then you can still use root disease preventatives like Phos 400 but add those just before you dump the recirculating hydroponic tank solution.

That way you can keep a residual of Oxine in the system at all times and still use Phos 400 in the nutrient solution and allow time for it to be taken up by the plants before the next dump.

The Phos 400 will deactivate the Oxine but this is not a big deal if Phos 400  is added 2 days before dumping.

Or apply the Phos 400 as a foliar spray only.

For indoor grow rooms Algae won’t grow on a dry surface. If you use flood and drain tables and the tables are taking a while to dry then you should be looking at the performance of your ventilation system to ensure they dry faster or look at turning off or covering any unused parts of your tables with Panda film so the unplanted, exposed surfaces don’t receive light.

Changing the total air volume 40 times per hour should be the minimum baseline for an indoor growing environment.

If you don’t reach that rate then all the other problems will follow: Wet or slow to dry tables (Algae), Poor transpiration rates, low CO2 (slow growth), high humidity (slow growth, fungal issues).

As more tables or plants are added to the system the problem will increase as there is more moisture being added to the air.

There really isn’t a magic bullet for algae as it will always seek to thrive if light and an exposed nutrient solution is available, but these notes will hopefully help in reducing the problem.