• 2 functions in 1 product
• Ceramic diffuser assures the best diffusing effect.
• Clear bubble reading provides accurate CO2 dosing.
• Made with acrylic assures long usage time.
• Compact size, easy assembling.

Features :

• Top quality ceramic assures the best diffusing effect.
• 2 in 1 functions of CO2 bubble counter and diffuser.
• Easy for ceramic replacement, cleaning and water filling.
• Acrylic material provides clear CO2 bubble reading and to be acid and breakage endured.
• CO2 pipe holder included to prevent CO2 pipe bending.

How to use :

• Loose the cap, take out the ceramic then fill up the reservoir with clear water then put back the ceramic and fasten the cap firmly.
• Connect the CO2 pipe to the CO2 inlet.
• Place the CO2 pipe holder below to the diffuser and secure the CO2 pipe to the CO2 pipe holder.

Specifications

What ISTA publish for the I-503 2 in 1 CO2 Diffuser M:

Function two in one — CO2 bubble counter and diffuser in one body
Diffuser ceramic
Body acrylic — acid resistant and breakage resistant, and clear enough to read the bubbles through
Size in the range M

ISTA sell four in this family: the I-685 cone S, the I-686, the I-503 M and the I-502 L. They are the same idea at different sizes.

What ISTA do not publish for this model:

• Dimensions and diffuser disc diameter
• The aquarium size or CO2 flow each size is rated for
• Maximum working pressure
• Reservoir capacity

Those rows are simply not on ISTA’s specification sheet or in their catalogue, and we would rather leave them blank than print a number we cannot source. If one of them decides your purchase, ask us and we will measure the stock item before you order.

Compatibility

It needs a regulator upstream of it, and a check valve. This is the far end of a CO2 line: cylinder, regulator or controller, check valve, then this. ISTA’s own instructions for the L size specify connecting a CO2 pipe with a check valve attached, and that is good practice for all of them.

It replaces a separate bubble counter. The counter is built into the body, so if you buy this you do not also need an in-line counter — though you still need the check valve, which this does not include.

Ceramic diffusers want pressure. Pushing CO2 through a fine ceramic disc takes more pressure than an open line does, which is why these are paired with pressurised cylinder systems rather than with a DIY yeast bottle. If your source is a low-pressure one, the disc will simply not mist.

ISTA publish no tank-size rating for any size in this family, so the S / M / L labels are relative to each other rather than tied to a litre figure. As a working rule the larger disc suits the larger tank, and we are happy to advise against your specific volume.

A CO2 pipe holder is included, and ISTA’s stated reason for it is to stop the CO2 pipe kinking where it turns down into the diffuser. A kinked line throttles the gas and makes a bubble count meaningless, so fit it rather than leave it in the bag.

Returns & Replacement

Returns are accepted within 7 days of delivery, provided the item is unused and in its original packaging. Manufacturer-sealed items cannot be returned once the seal is broken, and sale-priced items are not refundable.

If your item arrives defective or damaged, message us on WhatsApp with your order number, or email us if you would rather, and we will replace it. Approved replacements are delivered within 3 to 5 business days. Transit damage is covered by insurance on every shipment. If tracking shows delivered but nothing reached you, tell us within 72 hours, which is the reporting window Indian couriers allow. Damage caused during installation or use is not covered; replacement spares for such cases are chargeable.

Full terms are on our Cancellation & Returns page.