New · Hand-sewn & packed in the UK
Lower nitrate.
Clearer water.
No bleach.
Rechargeable resin filter bags that just sit in your filter and pull nitrate out of the water, day and night. When they’re full, recharge them with plain salt and go again.
From £30 · Free UK delivery · Posted within 2 working days
🧂 Recharge with salt
No bleach, ever
🧵 Hand-sewn
Tough PP mesh
📦 Free delivery
Mainland GB
Tested in my own discus tank
40ppm
Before
→
<5ppm
After
My tap water comes in at up to 40ppm nitrate, and for a long time my 540-litre discus tank sat at 40ppm or more. With these bags in the filter, it’s now under 5ppm.
Results from my own tank. Yours will depend on your water, stocking and maintenance.
Choose your bag
For most keepers, the Nitrate bag is the one to start with. Both sizes are flat, so water flows through the resin, not around it.
21 × 20 cm. For tanks up to about 500 litres.
18 × 15 cm. For tanks up to about 200 litres.
Start here
Nitrate
All nitrate resin, so it holds the most nitrate per bag. The one to choose if your tap water arrives high, or your tank keeps creeping up between water changes.
- Pulls nitrate out continuously
- Recharges with salt only
- Ideal for tanks on high-nitrate tap water
Also available
Nitrate + Clarity
Nitrate resin plus clarity resin in one bag. For tanks with bogwood or tannins, where the water also looks yellow or hazy. It holds less nitrate resin than the Nitrate bag, so if nitrate is your main problem, choose Nitrate.
Tank sizes are a guide. Heavily stocked tanks or very high-nitrate tap water will need recharging more often. Not sure which size? Email us with your tank size and filter.
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On sale now
The bags are live. Not ready to buy yet? Leave your email for discus tips, restock news and new products.
Need a different size or shape?
Every bag is hand-sewn, so I can make one to fit your filter tray, sump or reactor. Tell me your filter model or the dimensions you need and I’ll come back with a price.
Or email hello@discus-switch.com
How it works
1
Rinse & fit
Give it a quick rinse and lay it flat in your filter after the sponges. Fold to fit if you need to.
2
Let it work
The resin swaps nitrate out of the water as it flows through. Test weekly at first to see how it performs in your tank.
3
Recharge with salt
When nitrate creeps back up, soak it overnight in salt water, rinse, and put it back. No bleach, no special kit.
Questions
Will it fit my filter?
The 400g bag is 21 × 20 cm and the 200g bag is 18 × 15 cm. Both are flexible, so they fit most canister and sump filters. Lay it flat or fold it to fit the tray. The water needs to flow through it, not around it.
How often will I need to recharge it?
In my own 540-litre discus tank, on tap water of up to 40ppm nitrate, I run a custom bag with 400g of nitrate resin and 400g of clarity resin, and recharge it every few weeks. Yours could be more or less often, depending on how much resin you use, your tank size, stocking, feeding and how much nitrate is in your tap water. Test your nitrate weekly at first. When it starts creeping back up, it’s time to recharge.
Why salt and not bleach?
Many resins are recharged with bleach, which then has to be neutralised before the bag goes back in your tank. These bags are recharged with plain salt water: safer, cheaper and something you already have at home.
I have a planted tank. Is that OK?
Yes, but if you dose nitrate (for example with EI), the resin removes that too. Keep an eye on your nitrate and adjust your dosing, or use a smaller bag.
Can I leave it in while treating my fish?
No. Take the bag out before adding any medication, and leave it out until the treatment has finished and you’ve done your water changes. Resin can absorb some medications and stop them working. Keep it clean and damp while it’s out, then recharge it before it goes back in.
Does this replace water changes?
No. Water changes are still important for discus. The bag keeps nitrate down between changes and helps when your tap water is already high.
Delivery and returns
Free delivery to mainland Great Britain, usually posted within 2 working days. You can return unused bags within 14 days. See our terms of sale and returns.
Ready for lower nitrate?
Hand-sewn and packed in the UK by a discus keeper. Free UK delivery.
Questions? hello@discus-switch.com · Terms & returns