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General Troubleshooting

Tara | December 19, 2021
Seedlings close up

In Troubleshooting we discuss some of the more common problems that hydroponic gardeners may encounter. The below tips for treatment and prevention are offered as a guide only. For more personalised advice, visit our store or contact us.

Rust-like spots on leaves

Rust like spots can be caused by several things:

  • Fungus. Treat with a fungicide such as Fungarid. To prevent, do not overfeed/water or crowd your plants. Maintain consistent temperatures within the recommended zone (day temp 26 - 28°c and night temp 20 - 23°c) and ensure there is adequate ventilation.
  • Sap Suckers (Spidermite,Thrips, Aphids etc.). Examine the leaves for signs of infestation. Sap suckers feed on sugar, causing leaf tissue to die. This can present as rust-like spots. Treat with products such as Kryptomite, Mite Aerosol, or Mavrik. Prevent with predator bugs and check plants regularly to catch infestations early.
  • Necrosis. Necrosis can be triggered by several factors including over or under feeding, disease, and pests. Necrosis is the death of plant cells or tissues and can present as brown spots on leaves. To prevent necrosis, always check the EC of your nutrient solution and ensure your EC meter is calibrated correctly. If you suspect necrosis, separate infected plants from healthy ones. Remove the worst impacted leaves and avoid misting or foliar spraying the plant.
  • Deficiency. Nutrient deficiency can also cause brown spots. Other symptoms such as yellowing of the leaves, or discoloured roots may also be present. Prevent nutrient deficiency by using high quality nutrients and checking the EC of your nutrient solution. PH imbalance can prevent plants from taking up certain nutrients so, always keep your nutrient solution within the range of 6.0 – 6.6 (recirculating) or 5.5 – 5.8 for run to waste. Make sure you mix two part nutrients as directed and don’t forget to combine part A & B when required!
  • Phytotoxicity. Phytotoxicity is simply plant damage – a toxic reaction to something the plant was exposed to. Phytotoxicity can cause rust like aberrations. Other symptoms may include sick looking, yellowing or wilting leaves. Treat phytotoxicity by reducing the strength of your nutrient solution, and by avoiding additives and foliar sprays. Always make sure the nutrient solution is between 20-23°c.
If root disease is also present:
  • Add a fungicide such as Fungarid to the nutrient solution.
  • If scarid fly larvae are present, treat with a beneficial bacteria such as BAC Daily.
  • Once the scarid fly is eradicated, you will still need to use Fungarid to treat the infections they can leave behind.
  • Only use Fungarid for a week. Do not introduce benefical bacteria for 4-7 days after the use of Fungarid.
If root disease isn’t present:
  • Calibrate your EC and pH meters.
  • Ensure that you are not using expired or old nutrients (check the bottom bottles for signs of crystals and/or sediment).
  • Flush the plant with pH adjusted water before feeding again.
  • Check for signs of pests such as tiny spots on the surface and underside of leaves, holes in leaves, weblike fiber on the underside of leaves, or webs on the plants themselves.
  • Fungus could be the cause of the problem, which can be treated by spraying with fungicide.

Leaves Turning Yellow

Yellow leaves can be caused by several factors;

  • Incorrect nutrient solution temperature (keep solution between 18 -22°C). Use a water thermometer to measure nutrient temperature solution and use a water chiller if required.
  • Low oxygen levels due to lack of aeration in the nutrient solution. Aerate the nutrient solution using air stones or pumps.
  • Over-feeding (high EC). Always check the EC of your nutrient solution.
  • The onset of root disease. Treat with a fungicide such as Fungarid.
  • The pH is too high. Check the pH of your nutrient solution and adjust it if necessary.
  • Salt build-up. Treat with a product such as BAC Flush or House & Garden Drip Clean. Flush your system every 7-10 days. If using BAC Flush or H&G Drip Clean, flush every 2-4 weeks. Always flush with pH adjusted water @ 20-23 degrees C°.
  • Incorrect room temperature. Measure the room temperature and ensure it remains within the optimal zone (day temp 26 - 28°c and night temp 20 - 23°c).

All of these factors can prevent the plant from taking up nutrients in the correct quantities and balance.

Leaves Yellowing and Dying

If leaves are turning yellow from the bottom of the plant upwards – particularly in early flower, this is usually caused by root disease. Root disease is usually caused by oxygen starvation. Check the root system of the plant. If the roots are brown, it is likely caused by pythium, phytophthora, or oxygen starvation. A holistic treatment approach is required in these circumstances.

  • Oxygenate your nutrient solution with an air pump, air stones or a product such as Oxy Plus
  • Ensure the temperature of the nutrient solution is between 20-23°c
  • Reduce the strength of your nutrient solution to ½ the usual concentration and add a fungicide such as Fungarid for 1 week. Follow-up with preventative treatments containing beneficial bacteria such as BAC Daily.

Why are my plant’s roots brown?

Brown roots are an indicator of disease, likely pythium or phytophthora. Use a product such as Fungarid to treat root diseases.

Another frequent cause is over watering. Healthy roots should clearly be white. Products that promote healthy roots include RYZO and BAC Daily.

Tiny White Spots on Leaves

There are 2 main causes of white spots on leaves.

  1. A fungus/mildew. To treat, spray with a fungicide such as Fungarid.
  2. Aphids. Aphid infestations can appear as white spots. Treat aphids with a sucking insect spray such as Azamax.

Leaf Tip Burning

Tip burning is usually caused by excess salts. Excess salt can manifest in several ways:

  • Your nutrient solution may be too strong. Always check the EC of your nutrient solution and ensure your EC metre is calibrated.
  • You may have salt buildup around the root system. Treat with a product such as BAC Flush or House & Garden Drip Clean. Flush your system every 7-10 days. If using BAC Flush or H&G Drip Clean, flush every 2-4 weeks. Always flush with pH adjusted water @ 20-23 degrees C°.
  • Another factor that will affect salt levels is the size of your nutrient tank. In a recirculating system, the plants take up water and salts at different rates. Plants will absorb much more water than salt, leaving behind excess salt in in the nutrient solution as it recirculates. As a general rule, your nutrient tank should be large enough to ensure the nutrient/water volume decreases by only 10-20% each time you feed.

Leaf tip burning can also be caused by:

  • under-feeding
  • hanging your lights too close to your plants
  • not flushing regularly
  • nutrient deficiencies

Use a high quality nutrient and ask us for help with customising a method and schedule that meets your needs. As previously recommended, BAC Daily and BAC Flush will can assist in flushing out residual salts.

More Severe Burning

Severe burning can be caused by several factors:

  • Poor maintenance practices. Particularly in recirculating systems. Top up your nutrient tank regularly and test the pH daily. Always test the EC before feeding.
  • Your nutrient tank is too small. Remember, you want the volume of your nutrient tank to decrease no more than 20% each time you feed. The plants will generally take up a lot more water than salts. This can cause the nutrient solution to become very strong, which can burn the plants.

Leaf Curl Over

Leaves curling upwards can be caused by incorrect pH levels, which can lead to nutrient deficiency (particularly calcium deficiency). Incorrect pH levels can interfere with nutrient uptake. Check the pH of your nutrient solution and ensure that your meter is calibrated and working correctly. Also check your EC and your EC meter to ensure that you are giving your plants enough food.

Leaf Curl Under

Leaves curling under can be caused by over fertilization. However, again, this could be a pH related deficiency. Check that the EC and the pH are within range. Ensure that your meters are working correctly and that they are calibrated.

White Powdery Spots on the Leaves

This is likely a disease called powdery mildew (PM). PM spreads by air borne spores that enter the grow room from the ventilation or when the door is opened. To prevent PM, increase ventilation. Sulphur containing fungicides are the most effective treatment for PM. Prevent PM by ensuring your plants have a healthy immune system. Products such as BAC Daily stimulate a plant’s inbuilt immune system, improving overall plant health and increasing resistance to outbreaks of mildew.

Brown Rotting in the Flower Buds

This is likely a disease called botrytis (grey mould). To prevent botrytis, increase airflow in the room. Use clip fans and wall mount fans to increase airflow. Potassium silicate products (such as Quantum Silica) can prevent rot spreading through the flowers. Inspect flowers close to harvest to detect infections. Once botrytis has established itself in your crop it is almost impossible to control. Harvest infected flowers immediately, botrytis spreads very quickly.

Green Algae Growing on my Medium

Green algae is nothing to be concerned about. Green algae is caused by the reaction of light and water. Once the canopy of the plants develops, the green algae will stop growing.

Purpling of Leaves Towards the End of Flower

Leaf purpling is common towards the end of the flower stage. This is generally due to a Phosphorous deficiency. Mature plants can struggle to take up potassium and phosphorus.

Increasing the pH to 6.4-6.5 at this stage can help to alleviate this problem. We also recommend the use of PK boosters during flower. Try products such as BAC Organic PK Booster or Frooting Power.

Purple leaves can also be triggered if the environment is too cold.

Leaves Wilting

Leaf wilt often signifies excess heat. Particularly while the plants are young and fragile, excess heat can cause the leaves to wilt. Put a thermometer at plant height, under the lights, to measure the temperature around the plants. If you don’t have a min/max thermometer, check the temperature 2 hours after the lights come on and every three hours thereafter until the lights turn off.

Plants Yellowing and Looking Generally Unwell

Check your light timers. Incorrect light cycles can create a lot of problems for plants. If your light timers are OK, check the root systems of the plants to determine if the roots are brown.

Flowers Getting Offshoots

Offshoots are most often caused by light contamination during the ‘night’ period. Stay out of the room when the lights are off. Ensure your timers are working correctly. Ensure your plants are getting 12 hours of uninterrupted darkness.

Offshoots may also be caused by excess heat around the plants. Check the air temperature and increase ventilation if required.

Plants getting too big

There are several reasons your plants may be too big

  • You turned to flower too late. When you turn to flower (18hrs to 12hrs) too late, the plants will continue to stretch and grow for a longer period. 
  • Plant genetics. Some strains are not well suited for growing indoors.
  • Stress. In some cases, stressors can cause plants to behave differently than expected. For example, a hot grow room can cause overactive gibberellins resulting in exaggerated stem elongation. In this situation, a product such as Stop & Turn can effectively control a plants height.

Plants Stretching (Large Gaps Between Internodes)

Plants stretch for several reasons:

  • Insufficient light
  • Humidity is too high, or the room temperature is too high. Lack of ventilation is often the cause of high humidity/heat. A large fan may help to resolve this.
  • Too many plants in a small area.
  • Genetics. Some strains will have large gaps between the internode no matter what you do
  • Too hot during the plants’ nighttime. This is related to the hormonal activity within the plant.
  • Additives. The use of certain additives at the wrong times can cause problems. Stem elongation is largely due to gibberellin activity in the plant. The use of the wrong additives, at the wrong time can increase gibberellin production. In this situation, a product such as Stop & Turn can effectively control a plants height.
  • You turned to flower too late. When you turn to flower (18hrs to 12hrs) too late, the plants will continue to stretch and grow for a longer period. 
  • Stress. In some cases, stressors can cause plants to behave differently than expected. For example, a hot grow room can cause overactive gibberellins resulting in exaggerated stem elongation. In this situation, a product such as Stop & Turn can effectively control a plants height.
  • Low EC. A plant that is underfed will stretch. Check your EC levels and ensure you meter is working correctly.

Smaller Yields than Normal

This could be a result of many different factors, most of which are environmental.

If you haven’t changed anything, consider aging globes. Globes will burn brightly for 20,000 hours (in the case of HPS). However, while their lumen output may be reasonable, the colour spectrum drops out over time. As a result, the red spectrum that stimulates hormonal changes in the plant may not be quite what it was when you first purchased the globes. For this reason, it is advisable that you replace your globes every 12 months. Many growers replace them every third crop.

Small Bugs that Spin Webs

These are a troublesome pest known as Red Spider or Spider Mites. They can cause severe damage and should be treated by spraying plants to prevent infestation. Kryptomite provides 4 weeks of systemic protection against spider mites in earlier stage plants. If it is late in the flower stage, Mite Aerosol is recommended instead. For best results, do not use the same mite spray more than 3 times on the same cycle. Recommended treatments include Mite Aerosol, Kryptomite, and Kill-a-Mite.

Small Black Flies Around the Edges of my Pots, in the Coco, and Around the Root System.

The flies are probably Sciaria also known Scarids and Fungus Gnats. Left untreated, Scaria can easily kill a plant. Their larvae chew on and devour the fine root hairs of your plants; increasing the risk of waterborne diseases like Pythium. Gnatural is an effective Sciaria treatment. Fungarid may also be required to treat for common diseases caused by Sciaria. Sticky yellow fly traps can also be applied horizontally on the edge of pots to control and detect adult Sciaria.

Room Temperature is too High

High temperatures can create big problems for your plants. For example, oxygen starvation, reduced growth, and increased susceptibility to disease. There are several ways to reduce the temperature in your room:

  • Increase the airflow in your room with exhaust fans such as MAX FANS.
  • Purchase cooling devices for your globes such as cool tubes.
  • Add an air-conditioner. Refrigerated air-conditioning is the preferred option. Humidified air conditioners increase relative humidity levels, reducing transpiration and leaf cooling. If you must use a humidified air-cooler increase ventilation and keep an eye on humidity levels.
  • If your nutrient solution is too warm. Use a water chiller or move the tank outside the room if possible. You can also freeze bottles of water in plastic drink containers and throw these into the reservoir to bring down the nutrient temperature.

White Slime on Hoses in Nutrient Tank

This is caused by bacteria building up around the hoses in the nutrient tank. Sometimes this buildup can be very pronounced. This doesn’t always signal a problem. It depends on which types of bacteria are present in your nutrient tank. If you are using friendly bacteria, you needn’t worry. If you are using a sterilising agent such as hydrogen peroxide this bacteria shouldn’t be present.

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