Unit of alkalinity (alk) is dKH (degree of Carbon hardness), measured in dKH or ppm. Hope that clears up the confusion. If you are measuring alk (since you are dosing the big three), then you are measuing dKH.

Ok. This makes way more sense. KH is alk. Thank you. I was so confused for a bit there and now am more than a little embarrassed.

So I guess that my alk isn't causing any kind of problem with the bio-pellets and I should just soak them longer so they stop clumping at the top and maybe look into a better reactor. Does anyone having suggestions for a better reactor? Or should I just stick it out and use this one... or is it even worth using one when my phos is undetectable and have pretty low nitrates?

There are people who hates biopellets and then there are people who swears by them. Biopellets seems to be one of those things which, if you can make it work, works but otherwise screws up the whole tank. My experience with biopellets was bitter and hence I moved to zeovit.

Maybe post the values of your ca,alk and mg here and people will be able to help you more. Occasionally, wrong bacteria can start feeding on the biopellets and cause the system to crash so you have to make sure biopellet is being used by the right nitrifying bacteria but first and foremost important thing with any ULNS system is to make sure that the big three are in NSW range, alk being the most important one. It has to be between 7 to 8, you can probably push it to 8.5dkh. And tumbling is very important for biopellets.

There are quite a handful of biopellet reactors on the market so choose whichever is suitable for the amount of pellets you use and the size. I think vertex has some nice ones.

I see no reason to use biopellets if there is no issue with elevated NO3 or PO4. I swear by biopellets in situations where a tank needs to be cleaned up, but once a tank is cleaned up, biopellets aren't necessary or even particularly useful IMO. Biopellets can be very aggressive.

If you like the idea of a bacteria and carbon source system, check out Prodibio BioDigest and BiOptim. You only dose them once every 15 days (just pour it in the sump), and it is not aggressive like biopellets. Anecdotally, it seems to help keep the good bacteria population up which helps to keep bad bacteria populations down. I've been using it for a few years now.

I suspect that a probiotic system is not for you if you haven't yet gotten a firm grasp of the basics. That's just asking for a disaster.

If you're looking for a good biopellet reactor I'd recommend the Reef Octopus Biochurn reactors, such as the 90ext, it's a set it and forget it reactor and it's very easy to clean and maintain.

^-- this :-)

However, if you do decide to continue down this path, I would definitely echo a few things that were already recommended.

1. Soak for longer. I always soak for 24 hours or more. Be sure to stir occasionally.
2. A larger reactor. When I started using bioplets I used a TLF (Two Little Fishes phosban 150) reactor. It was OK to start out with but I still found it a challenge to keep the pellets tumbled. Those things are pretty small and I couldn't put a lot of pellets in them. I can't imagine using a smaller reactor than it. I eventually upgraded to a larger Vertext reactor that allowed me to pump more flow into the reactor. The key to getting the pellets to tumble is a sufficient flow rate from a feeding pump, plus room in the reactor chamber for the pellets to disperse/move.

There's been a lot of good info in here. Thanks everyone.

I am going to just keep doing what I am doing and soak my pellets longer. I will also look into getting a larger pellet reactor down the road. If anything goes weird again the first thing I'll do it turn of the pellets.

Since we're on the topic of bio pellets - how much should be in the reactor ?
Go by manufacture suggested amount or just keep testing nitrates ?

I only fill mine about once a year or longer. I pour in as much as the reactor can tumble easily, up to 1000 ml. The pellets gradually gets consumed until there is only a small amount left tumbling at the bottom. I check nitrates about once a month, and they are always zero.

Having said that, when you first start out, you want to go slow, maybe 2 - 300 ml to start and gradually build it up as the bio pellets start to work. That can take from several weeks to a couple months. This is when you should check nitrates more frequently and they should slowly come down to zero.

I decommissioned my bio pellet reactor a couple years ago, just to see what would happen. It took a couple months for the nitrates to gradually build up again. Then it took a couple months after I reinstalled it to get my nitrates back to zero. And my SPS weren't happy about that either.