ASM skimmer issues


Reaction score
I have a ASM G2 skimmer that will just flood about every 2 - 5 days. I have the gate valve mod on the skimmer and have the gate valve nearly opened all the way. The bubbles will barely be inside the cone, with a very modest amount of skimmate. A couple of days later I will check it and water will be flooding out the top of the container.

This happens about every 2 - 5 days. I've checked the air flow intake and it is fine, I've taken the pump apart and cleaned it as well as the entire skimmer with the same problem occurring shortly after.

I have a float valve for auto top off, I do weekly water changes of 10 gallons with reef crystals. My top off water is measuring 1 tds.

My tank is a 90 gallon with a 12 gallon rubbermaid sump. I have 3 fish 2 large carpet anemones and a mixture of sps corals. I cannot figure this one out.

I can't figure out if this is a water issue or a skimmer issue. I've had no deaths in months so it's not like something is decaying in the system.

I don't think its a water issue since I'm getting great growth out of my corals.

Anyone have any suggestions?

Question: how much fluctuation in water level occurs with your float valve top-off system?
Maybe a 100th of an inch, it constantly drips water in about a gallon a day.
Have you checked the exhaust of the skimmer for obstructions? That could cause the problem.
I usually check that once a day since I've been having this problem. I will run water through it to make sure that it is clean, or just put my finger on it to insure the bubbles move up.

I just reread your post, I can't say I've checked the exaust, but the opening is quite large.
The only time I've had this problem is when I added something abnormal. It always happens when I epoxy something. Also are you adding salt each day with your topoff water? That's the way you made it sound. You only need to add salt when you take salt out. Otherwise your salinity will keep increasing. Salt doesn't evaporate only water. You may not be adding salt it just seemed so in your post. Alot of times when salt is added like that it will cause the skimmer to act up.
It doesn't seem to be correlated with the water changes, and the top off is a float valve that adds only water from my RO/DI unit.

I recently changed from Instant ocean to Reef crystals, but I was seeing this problem prior to changing salt.

Using a refractometer, my salinity measures 1.024 temp is around 80. It could be an exaust issue, but why would this happen randomly?
If you could would you post a pic of your skimmer the way it is. I'm just curious if maybe its something I can see. I've had an ASM skimmer for about five years, actually I've had several versions and never had a problem unless I added something that caused the extra foam. You might want to drill a hole in the collection cup and put a fitting to overflow in a milk jug until you find out whats happening.
oils from your hands,frozen foods,phosphate removers,all seem to make my asmg3 go nuts sometimes.the past few months i had it running it was doing the same thing as yours.very finicky and quite annoying.
A couple of things to check: Does the impeller spin freely on the shaft and do the little rubber grommets at the ends of the shaft appear to be worn. Either of those things can cause inconsistent skimmer production and cause the problems you're having.
how often do you clean the glass on the tank...every time i clean my tank my asm it goes nuts..very wet skimmate...also noticed the water level in the sump has to be constant, otherwise it will mess with the output...i'd also suggest cleaning out the air intake by placing the tubing in some boiling ro/di water, to dissolve any salt particles that may have formed in the tubing. (you'll have to leave the pump on for it to suck the hot water through....)
I appreciate the ideas, just to clarify a few points. When the skimmer runs normal I get very thick dry skimmate. Then out of the blue the skimmer floods and what I mean by this is about a gallon of water a minute flowing out of the top of the skimmer. Almost violently.

If I was to drain this into a external bucket I would drain my tank in a matter of hours.

I thought I had it figured out a couple of weeks ago when I saw Tony selling his and saw the cap on the upper discharge. I was having issues with the skimmer getting back pressure, it appeared as if the skimmate was so thick it would cause back pressure on the discharge and force all the pumped water back out the discharge.
I don't have an ASM, however, I had a similar problem with a new skimmer. The impeller would seize intermittently causing it flood. So, I agree with mufret, check for signs of wear or binding on the shaft of the impeller. What kind of pump runs on that model?
i believe its a sedra 3500. Mine is doing the same thing Rhomer,it is very aggravating to have a cup of nasty skimmate one day then wake up the next day and have a volcano of water coming out of the collection cup.Im thinking about doing the recirc. mod and the meshwheel mod on the skimmer before i set it back up on my tank.
That was my first question as well... are you using the stock pump? How much flow are you pushing thru it?

Also on the cap on the gate valve mod... do you have a hole drilled in it?
No hole drilled in fact no cap, but I had a 1 1/4" ball valve lying around so I just used this. This would be simple to just open the valve slightly. I'm running the standard sedra 3500, I got this skimmer about a year ago. I just had the skimmer and pump apart a few weeks ago and cleaned the impellar, everything looked fine.

I don't have the recirc mod so the flow is the max flow of the sedra 3500.
were you having this problem before the "gate" valve mod?
what size ball valve are you using on the mod?
How deep is the water your skimmer is in?
I wasn't having this problem prior to the gate valve mod, but I did run the mod for about 3 - 4 months prior to having the problem. The water depth is about 8 - 10 "
Since I can't seem to upload images here arrggghhhhh. Here is the link to how I have the gate valve mod on my skimmer.