- Match grade, form and pre-soak needs to the method that will irrigate the medium.
- Convert a bed or a set of buckets into bags or blocks, checking the label’s expanded volume first.
- Run intake checks for dust, pH and salt before any medium enters the system.
01 / Specify the grade against the method
The media chapter compares materials by water, air and service; this guide covers the line on the order. A material name is not a specification. Oklahoma State’s Soilless Growing Mediums sheet (HLA-6728) says perlite is produced in grades, most commonly 0 to 2 mm and 1.5 to 3 mm in diameter, and mineral wool in everything from 1-inch cubes to huge slabs. Write the grade in millimetres and the form (loose, block, cube, slab).
The method fixes the grade before price does. HLA-6728 says of perlite: “Since it is very lightweight, it easily washes away. This drawback makes perlite an inappropriate medium in the flood-and-flush type of hydroponic systems.” Of clay pellets: “Because clay pellets float for the first few months until they’re saturated, the pebbles can get sucked into filters or drain lines and cause blockages.” So a flood bed takes coarse, heavy, pre-soaked material, and a net pot needs particles larger than its slots. UF/IFAS HS1488 starts lettuce in rockwool or foam grow cubes and HS1422 describes rock wool cubes with prefabricated seed holes, so for a raft or Kratky system the purchase is often a sleeve of cubes.
Reading: Soilless Growing Mediums (HLA-6728) ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗ · “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗
02 / Compressed versus loose volume
Loose media are sold by bag volume. Coir is usually compressed: HLA-6728 says the briquette requires soaking and “expands up to six times the size of the original briquette”. “Up to” is a ceiling, not an order quantity. Use the label’s expanded volume, and expand one block in a marked container before ordering the rest.
The arithmetic is original. A flood bed 1.2 m long, 0.6 m wide and filled 0.3 m deep holds 1.2 × 0.6 × 0.3 = 0.216 m³, or 216 L. In 50 L bags, 216 ÷ 50 = 4.32, so five bags. Ten drip buckets filled to 11 L need 10 × 11 = 110 L; with coir blocks labelled 70 L expanded, 110 ÷ 70 = 1.57, so two blocks.
03 / Dust, fines and the first rinse
Dust decides where the medium is opened. HLA-6728 says perlite dust “can create respiratory problems and eye irritation, necessitating precautions such as wearing goggles and a mask”; UF/IFAS ENH1359 recommends masks when handling large quantities of perlite and says fine vermiculite dust is irritating to inhale. Order a washed or screened grade when one is offered.
University of Minnesota Extension gives the intake step: “No matter which substrate you choose, soak it in water for 24 hours and change the water before transplanting your seedlings into it,” to remove dirt and debris and, in some cases, residues that can affect pH. As general practice, not from any cited document: rinse over a screen and keep rinse water out of the system and drain. Floaters after the soak go in contained pots, not a flood tray.
Reading: Soilless Growing Mediums (HLA-6728) ↗ · Common Media Used in Hydroponics (ENH1359/EP623) ↗ · Small-scale hydroponics ↗
04 / pH buffering and pre-treatment
Mineral wool comes with pH instructions; ask for them at purchase. HLA-6728: “The initial pH of the commercial material is rather high (7.0 to 8.0), therefore, continuous pH adjustment to a more favorable range (5.5 to 6.0) is required, or the medium must be conditioned by soaking in a low-pH solution before use.” HS1422 says most rock wool products require soaking in a prepared pH buffer solution to remove the natural alkalinity; ENH1359 gives its pH as 7–8.5 and says soaking instructions typically come from the retailer.
HLA-6728 gives clay pellets a pH of about 7.0 and says foam cubes have a neutral pH but no buffering capacity; ENH1359 gives coir 5.5–6.8 and vermiculite 7–7.5. None of these is a target for your solution. The check is original: measure source-water pH, soak a sample in it, and measure again. The shift, not the label, says whether pre-treatment is finished.
Reading: Soilless Growing Mediums (HLA-6728) ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗ · Common Media Used in Hydroponics (ENH1359/EP623) ↗
05 / Salt checks, source and food-crop records
Coir is bought against a salt question. HLA-6728: “If the husks are soaked in salt water during manufacturing and not rinsed with fresh water, then there could be a problem with high salinity.” It adds that coir must be washed and that calcium and magnesium are usually added to help remove sodium; ENH1359 says coir should be washed or rinsed before use because of the high salt levels common where coconuts are grown. Ask whether the bag was washed or buffered, and for the lot’s leachate EC. No cited document gives a pass or fail EC, so the check is comparative and original: expand a sample in a measured volume of source water, read EC before and after, and compare the rise between lots.
Source matters because the product varies. HLA-6728 says different sources and production procedures give coir a large variability on the market; University of Minnesota Extension calls coir a variable product and says untreated pumice may be hard to find. For a food crop, record supplier, origin and lot per bag, and check local rules; this guide makes no compliance claim.
Reading: Soilless Growing Mediums (HLA-6728) ↗ · Common Media Used in Hydroponics (ENH1359/EP623) ↗ · Small-scale hydroponics ↗
06 / Storage, reuse, disposal and the spec sheet
HLA-6728 says some media can be reused by pasteurizing at 180°F for 30 minutes or a 10% bleach soak for 20 minutes followed by multiple rinses; clay pellets can be washed and sterilized; mineral wool slabs can be reused by steam sterilizing between crops; vermiculite cannot be steam sterilized; mineral wool does not biodegrade. ENH1359 names sand, gravel, pumice and expanded clay as reusable, says media can hold pathogens from previous crops, and says rockwool cannot be reused and its disposal is a major issue (the two sources differ on mineral wool reuse; follow the product’s guidance). Store opened media dry and sealed, as general practice.
- Name the method and container, then set the grade and form it allows.
- Calculate container litres, divide by bag or label expanded volume, round up.
- Ask the supplier in writing for grade, washed or buffered status, expanded volume, leachate EC and conditioning instructions.
- Buy one bag or block. Soak it 24 hours with a water change, or follow the supplier’s conditioning instructions where they differ, and note the measured volume.
- Read source-water pH and EC, then soak-water pH and EC; record the shifts.
- Order the remainder from the same lot only when the measured volume, pH shift and EC rise are recorded and acceptable to you.
- Store dry and sealed; write the reuse or disposal route now.
| Criterion | What to write down | Where the figure comes from |
|---|---|---|
| Material, grade, form | Name; size in mm; loose, block, cube or slab | HLA-6728 grades; your net-pot slot size |
| Method fit | Flood, drip, net pot or plug; pre-soak needed | HLA-6728 on perlite and floating pellets |
| Volume | Container litres; bags or blocks; label versus test block | Your dimensions × depth; label |
| Dust and rinsing | Washed or screened; soak location; rinse-water route | HLA-6728, ENH1359; UMN 24-hour soak |
| pH pre-treatment | Instructions received; source and soak-water pH | HLA-6728 7.0–8.0; HS1422 buffer soak; ENH1359 7–8.5 |
| Salt | Washed or buffered; leachate EC; your before-and-after EC | HLA-6728 and ENH1359; your meter, comparative only |
| Source and lot | Supplier, origin, lot per bag; local rules checked | HLA-6728 variability; UMN |
| Storage, reuse, disposal | Dry sealed storage; reuse method or none; disposal route | HLA-6728 pasteurizing or bleach; ENH1359 reusable list |
FIELD QUESTIONTwelve 10 L drip buckets from coir blocks labelled 70 L expanded, and a flood bed 1.0 m × 0.5 m filled 0.25 m deep with 8–16 mm clay pellets in 50 L bags. What goes on the order?
Buckets: 12 × 10 = 120 L; 120 ÷ 70 = 1.71, so two blocks, ordered after one block has been expanded in a marked bin to confirm the label and its soak-water EC compared with source water. Bed: 1.0 × 0.5 × 0.25 = 0.125 m³ = 125 L; 125 ÷ 50 = 2.5, so three bags. Soak the pellets 24 hours with a water change, expect floaters because HLA-6728 says they float until saturated, and screen the outlet before the first flood. Record supplier, origin and lot for every bag.
Reading: Soilless Growing Mediums (HLA-6728) ↗ · Common Media Used in Hydroponics (ENH1359/EP623) ↗
Parts & buying criteria
Build your own parts & cost worksheet →
Showing ebb and flow. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Nutrient reservoir1 · illustrated quantity+
Stores the measured nutrient solution beneath or beside the growing area.
Inspect: Compare the surface with the pump intake or lower roots; freeboard is deliberate.
Maintain: Record level before refilling, keep light out and verify temperature, EC and pH.
Opaque, cleanable, intended-use container with volume marks and service access.
Check size, materials and operating conditions with your chosen supplier before ordering.02Pump & supply1 · illustrated quantity+
Moves nutrient solution from the reservoir to the growing area.
Inspect: Trace installed lift and branching; the pump label does not prove delivered flow.
Maintain: Measure output after service and inspect intake, filter and minimum water level.
Pump curve matched to installed head, required pressure and service needs.
Check size, materials and operating conditions with your chosen supplier before ordering.03Growing tray1 · illustrated quantity+
Contains supported media pots above the lower reservoir.
Inspect: Inspect the flood level, pot bases and accessible drain position.
Maintain: Verify full drainage and inspect moisture in representative pots.
Rigid cleanable tray with independent overflow and adequate support.
Check size, materials and operating conditions with your chosen supplier before ordering.04Root-zone mediumFor illustrated containers · illustrated quantity+
Stores moisture and air around the roots in the illustrated containers.
Inspect: Compare the medium surface with irrigation and drainage.
Maintain: Inspect wetting at several depths; prevent fines from reaching drains and emitters.
Prepared, stable grade matched to the irrigation method and crop.
Check size, materials and operating conditions with your chosen supplier before ordering.05Drain & overflow1 · illustrated quantity+
Returns drainage to the reservoir and provides a controlled high-water route.
Inspect: Follow the full slope and look for the separate high-level opening.
Maintain: Test pump-off drain-back and keep roots and medium out of the outlet.
Accessible fittings and verified capacity under normal and fault conditions.
Check size, materials and operating conditions with your chosen supplier before ordering.Evidence beside the lesson.
Source checks: September 2026. The geometry, inspection exercises and worksheets are original teaching material. The named organizations have not endorsed or reviewed this site.
Published recipe rates and planning ranges retain their source context. Calculator equations are accounting tools; they do not predict uptake, yield, toxicity or safe stocking. Model dimensions, water speeds, roots and fish counts are illustrative. Verify species, crop, source water and product labels for a real system.
- Oklahoma State University ExtensionSoilless Growing Mediums (HLA-6728) ↗
Physical properties and limitations of common growing media.
- University of Florida IFAS ExtensionGrowing Lettuce in Small Hydroponic Systems (HS1422) ↗
Lettuce system choice and management.
- University of Florida IFAS Extension“Set It and Forget It” Hydroponic Lettuce (HS1488) ↗
A small non-circulating lettuce example; seasonal and product assumptions apply.
- UF/IFAS ExtensionCommon Media Used in Hydroponics (ENH1359/EP623) ↗
Coco coir washed or rinsed before use because of high salt levels where coconuts are grown, pH 5.5–6.8; rockwool pH 7–8.5 with soaking to lower pH typically covered by retailer instructions, cannot be reused, not biodegradable and disposal a major issue; perlite dust and masks when handling large quantities; fine vermiculite dust, pH 7–7.5; expanded clay that can be washed, sterilized and reused; sand, gravel and pebbles, pumice and expanded clay listed as reusable media; media holding pathogens from previous crops.
- University of Minnesota ExtensionSmall-scale hydroponics ↗
Root support, transplanting, light, aeration and cleaning.
The next useful connections.
Ebb and flow: flood, drain, observe
Build a flood table, size its working water inventory and tune irrigation from the medium’s actual wetting and drying.
6 min + guided practice →Growing methodsDrip and Dutch buckets: deliver to every plant
Design a serviceable bucket system for larger crops, then measure irrigation uniformity and drainage.
Interactive tool · 6 min + guided practice →Media & propagationChoose media by water, air and service
Compare coir, mineral wool, expanded clay, perlite and propagation plugs in the system that will irrigate them.
6 min + guided practice →Media & propagationFrom seed to a working root system
Start consistent seedlings, establish root contact and transplant without importing avoidable problems.
6 min + guided practice →System designsMedia-bed aquaponics: grow without hiding the waste
Design an accessible aggregate bed, verify flood and drain behavior and preserve its biological function.
6 min + guided practice →