How to select RAS equipment

Start from the load, not the catalogue

Before choosing any unit, fix three numbers: design flow through the loop, peak daily feed, and water temperature. Every unit below is sized on one or more of them.

الترشيح الميكانيكي

Size the مرشح أسطواني on peak flow, with margin. Screen size sets what it catches: our standard is a 74 μm 316L screen. Where solids load is high, a settler ahead of the drum takes the heavy fraction and cuts backwash. Remove solids fast: the longer they stay in the water, the more they break down into fine particles and ammonia.

Finer is not always better. A 2025 trout trial found 45 μm gave better water quality than 70 μm, and 30 μm gave no further gain (DTU 2025). An earlier trial of 100, 60 and 20 μm found all three reached similar water quality in long-term operation (Aquacultural Engineering 2015). Screen size is a trade-off with flow per drum and backwash water.

Fine solids and organics

In marine and shrimp systems, and dense freshwater ones, a مزيل البروتين lifts out what the screen cannot catch. Pairing it with ozone raises removal.

الترشيح البيولوجي

Size the مرشح حيوي MBBR on peak daily feed, not tank volume. Cold water and saltwater slow nitrification, so those systems need more media. Allow time for the biofilter to mature: see the start-up guide.

تبادل الغازات

Dense systems build up CO₂. A برج إزالة الغازات removes it before oxygen goes back in. Cold-water species are often given a CO₂ tolerance of about 10–20 mg/L and warm-water species about 20–40 mg/L (FloNergia). Size oxygen supply on the demand after feeding, the peak of the day, and include a standby. A common rule of thumb is about 350 g of oxygen per kg of feed for the fish (Novair). PSA generators make oxygen on site and مخاريط الأكسجين dissolve it with high transfer.

التطهير

معقمات الأشعة فوق البنفسجية sit on the return line after solids removal, sized on flow and water clarity. Clear water matters: solids shield pathogens from the light.

التكرار

Decide which units the farm cannot run without for an hour: usually circulation pumps, blowers and oxygen. Give each a standby.

Check the balance, not the boxes

A drum filter, biofilter and oxygen system can each be correctly sized and still fail together, if they were sized on different flows. When stages come from different suppliers, ask who is responsible for the flow balance between them. Send us your equipment list and we check the sizing before we quote.