Welcome to the Rock 'N' Critters blog!

This is where you'll find all of our latest updates, as well as insights from our marine aquarium experts. If there's a topic you'd like to see us cover in a future blog post, please feel free to get in touch!


In this blog post we are going to cover the different types of Aquarium designed specifically for keeping marine fish. What are the different types, what makes them different from each other and some information to help you make a more informed choice if you're just getting into the hobby. By the end of this blog you'll know your Nanos from your Peninsulas! 


Copepods are small aquatic crustaceans which inhabit a vast range of salinities from fresh water to hypersaline conditions. They are found all over the planet in virtually all bodies of water so, naturally they form a significant foundation of the aquatic food web. For many fish, copepods are the preferred food source and some will feed almost exclusively on them such as the Mandarin fish. For most other fish, copepods make a great addition to their diets. Copepods are incredibly small but not microscopic! So you won't need a microscope to see them although if you're looking for them with the naked eye you won't see much more than a small white speck or dot on the glass. The glass of your aquarium is the best place to see them, look for small specks which move around, chances are these are copepods. Just because you can only see them on the glass doesn't mean they aren't existing throughout your aquarium though. They will be on the sand, rockwork, coral and equipment; they just wont be as visible there as they are on the glass. 

You can add copepods from packs of live copepods such as these which will help to establish a self sustaining colony. Your best bet to establish a colony of copepods is to use live rock or failing that, you will likely have more success in a more established reef aquarium. You can also culture your own by keeping a small tank of saltwater separate to your reef system and then adding live copepods with a few drops of phytoplankton before leaving nature to take its course. The copepods will breed and you'll have a supply you can dose to your tank. The other option is if you have a refugium you can add live copepods directly to this and let nature take its course again. If you have fish which actively eat copepods then you will likely need to replenish your copepod colony regularly. A way of monitoring your colony levels is by keeping a mental track on the rough levels of copepods on the glass. When you see less or no copepods on the glass you know you're running low and need to bump up the numbers a bit. 

So to sum up, copepods are great to have in your reef. You can add live copepods and cultivate your own colony but its always worth keeping an eye on the colony levels in the aquarium. 

And if you want to read more information about pods, then follow the link below to the 'What Are Pods?' blog post; 



Here in the UK we are most often concerned with heating our marine aquariums up to temperature but what happens during heatwaves like the one we've just experienced. How do we keep our aquariums at the right temperature and stable? Here are a few things you can do to mitigate the summer hot spells.


What is Salinity, why is it important, what role does it have to play in the marine aquarium and finally, how do I test it?


'What substrate should I have in my reef tank? Should I go bare bottom or deep sand bed? Gravel or sand, fine sand or course sand? What does it all mean, what should I do?' Let's look through what the substrates are, its function and what it means so that you can make the informed decision of what you want to do. Let's go. 


All too often on social media I see people posting pictures of 'specks' on the glass or small invertebrates with the caption 'can anyone ID these'. The answer that often comes in the comments section is 'pods' which whilst not often wrong isn't always that helpful. So, this blog is all about answering the question, What are pods?

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Pods are a generic name used by reefers to describe small fauna in the aquarium which often live in the sump, rockwork or on the glass of the aquarium. When social media commenters use the term Pod they are most often referring to either Amphipods and Copepods, hence the name 'Pods'. So when the answer Pods is given to an identification question, it's not often wrong but it could be more exact. So let's quickly break it down into the two main type of Pods that you are likely to see in your aquarium. 


As you can see in the picture these are small shrimp like invertebrates which will live on your rockwork in the main display or in detritus in your sump. They can use their appendices to propel themselves through the water column but most often they'll be scuttling around on the rockwork as if they weren't underwater at all. They can grow to be about a cm in length and some will have brown bands on their body whilst others will have black bands. The best time to see these pods is at night time with a red torch. Wait until you lights go out and then give it a few hours before using the red torch to look around the rock work and chances are you'll catch them running about. Ultimately, they are a good part of the overall eco system in your reef and will form part of your clean up crew, plus they are free fish food.. if the fish can catch them!  


Copepods are a lot smaller than Amphipods and look more like tiny white specks on the glass of your aquarium. If you can see them on your glass then they will certainly be in the rockwork as well however it's quite hard to see them on the rockwork so you'll always notice them on the glass first. The largest that Copepods really get is the size of the tip of a ball point pen. They really are tiny! Again, they are a great part of your reef tank ecosystem and if you have loads of them on your glass then they are a tell tale sign that your reef is going really well. They will naturally form some part of your clean up crew but best of all, they are a live food source for your fish. I often see my clownfish cruising the glass pecking off copepods one at a time. Some fish feed exclusively from Copepods such as the Mandarin Fish which is why everyone stresses that you must have a big supply of Copepods in your reef before attempting to keep one. They will plough through your Copepod population like there's no tomorrow!


These aren't pods strictly speaking but they microscopic organisms which I thought were worthy of a quick mention. They are much the same as Copepods and will form a valuable part of the reef tank clean up crew. They're also free fish food if your fish can catch them. Frozen or Liquid rotifers can be bought as a food source for your reef tank but these will of course not be live food. Rotifers will naturally colonise your reef tank over time, especially if you start with Live Rock but unless you have a microscope, you won't see them or positively identify them. Just know that they are there and that they're a good thing. 


If you've never noticed any pods in your marine tank before then go have a look! I bet they're there, you've just never noticed them before. I mean, they are pretty small so you'd be forgiven for missing them. Use a red torch to look in your main tank at night and you can get away with a white torch in the sump (white light at night may spook your fish and distress them so always be wary of this). If you can't find any and you'd like to add some or maybe you want to boost your current population then bags of live Copepods are sold in store. Just float the bag in your tank for 10 minutes for the temperature to equalise and then dump them in. If you have some rock rubble in your sump then dump some here too. They'll establish themselves over time and begin breeding. 


So that is a very quick whirl wind tour of 'Pods'. Now when you see the answer Pods you'll be able to dig into it a little more and figure out if it's Copepods or Amphipods. Just remember that they're both good things for your reef tank so don't panic thinking you have a pest. 

What are Automatic Filter Rolls? What do they do? How do they work? Should I get one for my setup? In this Blog we're going to look at automatic filter rolls, the pros/cons and answer all of those questions you have about them.


What is a frag? 

A frag is just like a plant cutting. It is a piece of coral which has been broken off or cut from a larger piece of coral to grow into a large coral all over again. It isn't a new coral to be exact but rather an exact copy of the original coral from which the frag came. The polyps of the coral will clone themselves and over time will grow into a copy of the original. Fragging corals is a great way to keep on top of corals which are getting too big and also makes for a cost effective way of adding corals to your reef because a frag will always be less expensive than buying the original larger coral. You can get coral frags of SPS, LPS and Soft Corals.


There are frags on the RnC website which can be found at the link below;


And if you want to read more information about frags, the pros and cons, then follow the link below to the Frags 101 blog post; 


What is a Coral Colony?

A Coral is an animal with a calcium carbonate skeleton covered in tissue and polyps. These polyps can be either small or large depending on the type of coral, hence LPS - Large Polyp Stony coral or SPS - Small Polyp Stony Coral. These polyps are identical to one another and replicate when the coral grows. They essentially 'colonise' an area on the reef by asexual reproduction which gives way to the name 'Coral Colony'. In the hobby we tend to use the term colony to define the size of a coral which can be quite subjective depending on who you speak to. A generally well accepted definition of what constitutes a colony is when the coral visually represents what the natural growth form of the coral is at its full size. This is easier for the likes of Acropora where one branch would be a frag and multiple branches which look just like a miniature version of the larger coral would be considered a colony or specifically in this scenario a 'mini colony'. It's more difficult for corals like Favia or Montipora where the growth is flat and encrusting. Defining 'colony' size of this coral is subjective but I would say it's somewhere around the size of a coffee coaster or larger, but again this is really subjective.