Apex Grow
Hydroponics
Hydroponic Troubleshooting Index
Answers to the most common hydroponic problems, organised by category. Each entry gives you the direct fix. Click through to the full guide for step-by-step detail.
1. Pests and Diseases
- 1.1 Spider Mites
- 1.2 Diatomaceous Earth for Gnats
- 1.3 Fungus Gnats
- 1.4 Scale Insects
- 1.5 Powdery Mildew
- 1.6 Aphids
- 1.7 Mealybugs
- 1.8 Thrips
- 1.9 Root Rot
- 1.10 Grey Mould (Botrytis)
2. pH, EC and Water
3. Nutrients
4. Pumps and Aeration
5. Environment and Reservoir Issues
6. Plant Growth and Yield
1. Pests and Diseases
1.1 Quick Answer: Spider Mites in Hydroponics
- Spider mites are arachnids, not insects, so most standard insecticides have little effect on them.
- First sign is usually pale or yellow speckling on the upper leaf surface; check the underside of leaves for the mites themselves and fine webbing.
- Treat with a miticide like Mite-Rid, rotating products between applications so mites don't build resistance.
- Spray during the lights-off period and remove the worst-affected leaves before treating.
- Prevent by keeping humidity above 60% RH and temperatures below 25°C, conditions mites don't thrive in.
Full guide: Spider Mites in Australian Grow Rooms · Shop pest control products
1.2 Quick Answer: Does Diatomaceous Earth Kill Fungus Gnats?
- Diatomaceous earth only works while completely dry, and loses its effect the moment growing media gets wet.
- In an actively watered hydroponic system, media is wet most of the time, which is why DE alone often under-performs.
- A moisture-resistant product like Gnat Nix holds up far better as a top dressing in wet conditions.
- Letting the top layer of media dry out between waterings also interrupts the gnat larval lifecycle directly.
Full guide: Diatomaceous Earth for Fungus Gnats · Shop Gnat Nix
1.3 Quick Answer: How to Get Rid of Fungus Gnats
- Adult gnats are mostly a nuisance; it's the larvae living in the growing media that actually damage roots.
- Let the top layer of media dry between waterings to break the larval lifecycle.
- Combine sticky traps for adults with a larval treatment like Gnat Nix applied to the media at the same time.
- Treating only the adults without addressing larvae in the media means the problem returns within days.
1.4 Quick Answer: Scale Insects on Hydroponic Plants
- Scale appear as small raised bumps or a waxy coating on stems and leaves, easy to mistake for a plant feature early on.
- A horticultural oil or insecticidal soap works by suffocating them on contact; thorough coverage matters more than concentration.
- Repeat treatment every 7 to 10 days, since a single application rarely gets every insect and egg.
- Prune away heavily infested stems rather than trying to treat them in place.
Full guide: Scale Insects on Plants · Shop pest control products
1.5 Quick Answer: Powdery Mildew in the Grow Room
- Powdery mildew spores are present in ambient air almost everywhere, so the goal is preventing the conditions it needs, not excluding exposure entirely.
- Keep humidity below 50% during late flowering, when plants are most vulnerable.
- Treat at the very first sign of white powdery patches with a product like Micro Kill rather than waiting for it to spread.
- Rotate treatment products between applications to avoid resistance building up.
Full guide: Powdery Mildew Prevention and Treatment · Shop Micro Kill
1.6 Quick Answer: Aphids on Hydroponic Plants
- Aphids are soft-bodied sap suckers that cluster on new growth and the underside of leaves.
- A botanical spray like Zero Tolerance is one of the most effective natural treatments readily available in Australia.
- Yellow sticky traps placed near the canopy catch winged aphids before a colony has a chance to establish.
Full guide: Aphids on Hydroponic Plants · Shop Zero Tolerance
1.7 Quick Answer: Mealybugs in Hydroponics
- Mealybugs show up as white waxy powder with cottony egg masses, usually in leaf joints and along stems.
- Isopropyl alcohol, diluted with water, applied directly to individual insects with a cotton swab dissolves their protective wax coating on contact.
- Check leaf joints and stem crevices carefully, since mealybugs hide in gaps that sprays alone can miss.
Full guide: Mealybugs on Hydroponic Plants · Shop isopropyl alcohol
1.8 Quick Answer: Thrips in Hydroponics
- Thrips damage shows as silvery streaking and distorted new growth, often before you spot the insects themselves.
- Treat during the lights-off period and target the underside of leaves where thrips shelter.
- Blue sticky traps catch thrips more effectively than yellow, since thrips are more attracted to blue.
Full guide: Thrips on Hydroponic Plants · Shop pest control products
1.9 Quick Answer: Root Rot in Hydroponics
- Almost always caused by Pythium, a water mould rather than a true fungus, so antifungal products don't treat it effectively.
- Healthy roots are white or cream and firm; infected roots turn brown or grey with a slimy coating and a fishy or sewage-like smell.
- Reservoir temperature is the biggest risk factor: above 22°C dissolved oxygen drops, and above 26°C Pythium can take hold within 24 to 48 hours.
- Act immediately: drop reservoir temperature, boost aeration with air stones, trim away affected root tissue, and treat with Oxy Plus.
- Prevent recurrence with full system sterilisation using Guardian Hydro Clean between grows.
Full guide: Root Rot in Hydroponics Australia · Shop aeration products
1.10 Quick Answer: Grey Mould (Botrytis) on Flowers
- Botrytis needs both high humidity and dead or dying plant matter to get established.
- Genetics play a major role. Some strains and phenotypes are naturally resistant to botrytis, while others are highly susceptible almost regardless of environment.
- Keep humidity around 55% RH during late flowering, when developing buds are most susceptible. This is a realistic practical minimum for most grow spaces rather than an extreme target.
- Besides genetics, the two biggest factors are keeping air actively circulating through the grow space with an oscillating fan or other climate control equipment, and removing any dead or dying leaves promptly. This matters especially for leaves near or directly on bud sites, since these are the most common infection points.
- If botrytis keeps recurring despite good airflow and hygiene, proper research into your specific genetics is the best starting point. Some genetic lines are simply far more prone to mould regardless of how well the environment is managed.
Full guide: Botrytis / Grey Mould in Flowering Plants · Shop Micro Kill · Shop climate control
2. pH, EC and Water
2.1 Quick Answer: Why Does My pH Keep Dropping?
- Falling pH is most often driven by nutrient uptake patterns and, later in a grow, by decaying root matter in the reservoir.
- Check for early root health issues first, since a dropping pH can be an early warning sign of root problems before other symptoms appear.
- Correct with a pH Up product, but treat the underlying cause rather than just chasing the number daily.
Full guide: Why Does My Hydroponic pH Keep Dropping? · Shop pH Up & Down
2.2 Quick Answer: Can I Use Australian Tap Water for Hydroponics?
- Yes, you can use tap water for hydroponics in Australia, but its suitability varies significantly by city and region.
- Hard water regions typically push pH upward and add background EC before you've dosed any nutrients at all.
- Test your specific source water's pH and EC with a reliable EC meter before assuming a standard feeding schedule will apply as written.
Full guide: Australian Tap Water for Hydroponics · Shop pH & EC products
2.3 Quick Answer: Why Is My pH Meter Giving Inconsistent Readings?
- Most inconsistent readings come from the probe, not the water. Recalibrate weekly using fresh pH buffer solution, not old or contaminated solution.
- If readings still drift after a fresh calibration, the probe itself may be reaching end of life and need replacing.
- Always store the probe wet using a proper probe care kit between uses; letting it dry out damages the sensing membrane permanently.
Full guide: Why Is My pH Meter Giving Inconsistent Readings? · Shop calibration kits
2.4 Quick Answer: What EC Should I Run?
- Target EC depends on crop type and growth stage, generally lower during seedling/clone stage and higher through vegetative and flowering.
- Evaporation concentrates the nutrient solution faster than plants take it up, so EC creeping upward over several days is expected, not a fault.
- Top up a rising reservoir with plain water rather than more nutrient solution, checked with a digital EC meter.
3. Nutrients
3.1 Quick Answer: Nutrient Lockout (Deficiency Despite Correct Feeding)
- If plants show deficiency symptoms despite a correctly mixed feed, check pH first. Most lockout is a pH problem blocking uptake, not an actual nutrient shortage.
- Salt buildup in the growing media over time can also block nutrient uptake even when the reservoir solution itself is correct.
- A full flush with plain, pH-adjusted water clears salt buildup and gives you a clean baseline to re-diagnose from.
3.2 Quick Answer: Cal-Mag Deficiency
- Calcium and magnesium deficiency shows as interveinal chlorosis (yellowing between leaf veins) and is most common on RO or naturally soft water.
- High-intensity LED lighting increases a plant's calcium and magnesium demand, making deficiency more likely even on otherwise adequate feed.
- A dedicated Cal-Mag supplement corrects this faster than adjusting base nutrient ratios alone.
Full guide: Cal-Mag Deficiency in Hydroponics · Shop Cal-Mag
3.3 Quick Answer: Nutrient Burn vs Transplant Shock
- Nutrient burn shows as crispy, browning leaf tips and edges, typically starting on the oldest, lowest leaves first.
- Transplant shock shows as general wilting and slowed growth shortly after moving or disturbing a plant, without the crisped leaf-edge pattern.
- Telling them apart matters because the fixes are opposite: nutrient burn needs a flush and reduced feed strength, transplant shock needs time and stable conditions, not less feed.
Full guide: Nutrient Burn vs Transplant Shock · Shop base nutrients
4. Pumps and Aeration
4.1 Quick Answer: Why Is My Water Pump Not Working Properly?
- A humming pump that isn't moving water usually indicates an airlock or a jammed impeller, not a failed motor.
- Mineral crystallisation from hard water can build up on the impeller over time and restrict flow gradually rather than suddenly.
- A pump left running dry, even briefly, can damage the seal. If it's beyond repair, a reliable replacement like the Rio HF submersible pump is a solid upgrade.
Full guide: Why Is My Water Pump Not Working Properly? · Shop water pumps
4.2 Quick Answer: DWC Bucket Losing Oxygen or Smelling Bad
- A bad smell and declining plant health in a DWC bucket usually means dissolved oxygen has dropped low enough for anaerobic bacteria to take hold.
- Check the air stone for clogging first, since a partially blocked stone reduces oxygen output well before it fails completely.
- Increasing air pump output and dropping reservoir temperature both raise dissolved oxygen levels directly.
5. Environment and Reservoir Issues
5.1 Quick Answer: Why Is My Reservoir Turning Green?
- Green water almost always means algae, and algae needs light reaching the nutrient solution to establish, not just moisture and nutrients which are already present.
- Common light leaks: lid edges that don't seal flush, net pot gaps, clear tubing, sight tubes, and light-coloured or clear reservoir walls.
- Full light exclusion is the actual fix. Cleaning algae without sealing the light leak usually means it's back within days.
- Use fully opaque reservoirs like the Tub 65L Black, opaque tubing, and a properly sealed lid to prevent it establishing in the first place.
Full guide: Algae and Light Leaks in Hydroponics · Shop opaque reservoirs
5.2 Quick Answer: Sterile or Bioactive Reservoir Management?
- A sterile approach uses oxidisers like Oxy Plus to suppress microbial activity broadly. A bioactive approach introduces beneficial bacteria like Azos or fungi like Mykos to the root zone.
- Oxidisers aren't selective. They don't distinguish between pathogens and the beneficial bacteria you're trying to establish.
- Don't introduce beneficial bacteria while an active oxidiser is present. It will undermine the biological treatment before it has a chance to work.
- Pick one primary strategy and only switch between cycles, with proper cleaning in between.
Full guide: Sterile vs Bioactive Reservoir Management · Shop Oxy Plus
5.3 Quick Answer: Cleaning Biofilm From Hydroponic Lines
- Biofilm is attached microbial and organic material that builds up inside wet tubing, drippers and fittings, not something floating loose in the reservoir.
- Signs of buildup include uneven flow between outlets, gradually declining flow, a slippery internal residue, and an off smell from tubing or fittings.
- Isolate the affected plumbing section rather than running strong chemicals through lines still connected to living roots.
- Start with plain water, disassembly and physical cleaning with a soft brush before considering anything stronger.
Full guide coming soon. · Shop fittings and drippers
6. Plant Growth and Yield
6.1 Quick Answer: Why Are My Tomatoes and Peppers Not Fruiting?
- No flowers at all usually points to plant maturity, insufficient light, temperature stress, or excess nitrogen delaying reproductive growth.
- Flowers that form but then drop point toward environmental stress, root-zone stress, or a pollination problem rather than a nutrient issue.
- Self-fertile flowers like tomatoes and most peppers can still fail to set fruit indoors without enough air movement to trigger pollen release.
- Diagnose which stage is actually failing, no flowers, flower drop, or fruit that doesn't develop, before changing your nutrient program.
Full guide coming soon. · Shop Cal-Mag
6.2 Quick Answer: Why Are My Seedlings Stretching?
- Stretching usually means light is too weak, too far away, or unevenly distributed across the tray, causing the seedling to grow upward searching for light.
- Leggy seedlings show a long, thin stem with unusually large gaps between leaf sets, rather than compact growth.
- The stem that has already stretched won't shorten back down, but correcting conditions improves all future growth from that point on.
- A dedicated propagation fixture like the SANlight FLEX II is built for the correct seedling intensity range from the start.
Full guide: Seedling Stretching and Light Height · Shop propagation lighting