Reverse Osmosis Water (RO) & Salt Mixes

At Birchwood Aquatic Centre, we know that the key to crystal-clear, healthy aquariums starts with quality water. That’s why we offer professionally filtered Reverse Osmosis water (RO) and pre-mixed marine saltwater — ready for you to use straight away. Our RO water is produced on-site using advanced multi-stage filtration systems that remove chlorine, heavy metals, phosphates, nitrates, and other impurities commonly found in tap water. The result is ultra-pure, zero-TDS (Total Dissolved Solids) water which is perfect for tropical, freshwater, shrimp, and marine aquariums.

Reverse Osmosis Water (RO) – Ideal for Freshwater & Top-Ups

RO water is ideal for:

  • Freshwater fishkeepers who want stable, clean conditions
  • Topping up evaporated water in marine and reef tanks (without altering salinity)
  • Mixing with tap water to achieve precise hardness and pH levels
  • Breeding soft-water species such as Discus, Angelfish, or Dwarf Cichlids

Available in 10L, and 25L containers – bring your own or purchase one of our reusable jerry cans in-store.

Important: RO water should only be used for topping up evaporation or when remineralised for freshwater use. Using pure RO water alone for full water changes can crash your system by removing essential minerals and buffering capacity, causing dangerous pH swings.

Pre-Mixed Saltwater – Ready to Use

For marine and reef hobbyists, we supply pre-mixed saltwater made from our pure RO water and premium-grade reef salt, ensuring consistent salinity, trace elements, and mineral balance every time. Our mix is ideal for reef aquariums and marine fish systems. 

Our saltwater is perfect for:

  • Water changes in reef and marine aquariums
  • New tank setups
  • Emergency top-ups or quarantine tanks

Why Choose Our Reverse Osmosis (RO) & Salt Mixes?

  • Professionally filtered with multi-stage RO membranes and deionisation
  • Tested regularly for TDS and purity
  • Consistent salinity and chemical balance in every batch
  • Convenient refill service – eco-friendly and affordable
  • Expert staff on hand to help calculate how much you need

Bring Your Containers or Use Ours

We encourage customers to reuse containers to reduce plastic waste. Simply bring your own clean container, purchase one in store or borrow (for a deposit) one of our food-grade jerry cans in-store.

Get the Right Start for Your Aquarium

Whether you’re setting up a new tropical tank, maintaining a reef system, or just need top-up water, our high-purity RO and salt mixes make it simple. Pop into Birchwood Aquatic Centre, Swanley, and we’ll help you get exactly what your fish need.

Frequently Asked Questions

Not without remineralising it first. Pure RO water lacks essential minerals and buffers, which can cause your tank’s pH to drop suddenly. Always mix RO water with a suitable remineralising product or combine it with a percentage of treated tap water.


Only when water has evaporated. As water evaporates, the salts and minerals remain, so topping up with RO water keeps salinity and hardness stable. Do not use it for full water changes unless adjusted with minerals or salt mix.


Tap water can contain chlorine, chloramine, heavy metals, phosphates, and nitrates that may harm sensitive fish and plants. RO water gives you complete control over water chemistry, making it perfect for aquarists who want stable, clean conditions.

We sell 10L, and 25L cans. You’re welcome to bring your own clean containers, or you can purchase our 5L or 10L reusable food-grade jerry cans in-store.


Pre-mixed saltwater can be stored for up to 2–4 weeks if kept sealed and in a cool, dark place. Stir or aerate before use to reoxygenate and ensure the salt is fully dissolved before adding it to your aquarium.


No — always top up with pure RO water only. Using saltwater for evaporation top-ups will increase salinity over time, which can stress or harm marine life.

Absolutely! Bring your own clean container, purchase the container from us or borrow (for a deposit) one of our reusable 10L or 25L jerry cans in-store. We encourage refills to help reduce plastic waste.