Let me start by saying im new to this forum. Im having problems with my 55g jack dempsey tank and was hoping someone here could help.
I have a 55g with a undergravel filter and a powerhead hooked up to it. I also have a external filter hanging on the back. Im not sure what size but its big enough because my old piranha was in this same setup for a couple years before dying of old age. I never had any problems with my piranha.
After my piranha died i cleaned everything and got new rocks and stuff. I bought 2 baby electric blue jack dempseys. One died after 6 months. He was always laying on the bottom of the tank so i did a water change and he was dead the next day. The pet store tested my water and said it was fine. The other jack died 2 months later and the pet store said my ph was a little high at 8.4. Theres also a pleco in the tank who doing just fine.
Now i want to replace them with a full grown jack but i want my ph and everything to be right first. Iv read all about the nitrogen cycle but dont understand really. The fish craps and this turns into that and that turns into this and its bad so it needs to be filtered. But theres also benifitial bacteria?
Anyways how do i:
Lower/raise ph and everything without the confusing talk?
And how to i syphon the rocks for my undergravel filter? I usually only syphon the front or back half at a time. is this correct or should i do it all?
O and i have no plants.
Alot to read i know but any help would be great.

Absolutely the first thing you need to do is buy yourself a test kit.
The strips are very inaccurate, I recommend the freshwater test kit from API.
YOU need to be able to accurately test the water anytime needed.

Ph isn't nearly as important as ammonia and nitrite levels.

Here is a quick basic discription of the cycle.

Fish waste, and non eaten food decomposes to become ammonia.
Ammonia becomes nitrItes, and nitrItes become nitrAtes

Ammonia and nitrItes will kill fish. High levels of nitrAtes will also, water changes get rid of nitrAtes.

"Good bacteria" is what breaks down the harmfull substances and forms the cycle.

By cleaning and replacing everything you likely destroyed the good bacteria and the cycle has to start all over.

You will not be able to keep fish alive in there very long without knowing what your water quality is, especially if it is going through a cycle.

Some fish are more resistant than others.

Live plants will help lower PH
Check the PH of your tap water. If it is at acceptable levels, then a simple water change will lower the PH.

__________________
150G, 1 shovelnose sturgeon 8", 1 polypterus endilicheri 9", 1 leopard ctenapoma 4", 1 Distichodus Sexfasciatus 6", 1 Farlowella acus algae eater 8", 2 silver dollars, 2 tank bred angelfish, 1 clown knife 11", 1 Jaguar hybrid syntadonis 4", 6 African cichlids 3+"

Ok ill buyi kit. Right now im using strips. I havnt had a problem with nitrate or anything. After the 2nd jackdied the ammonia went up a little bit but im thinking it was just because of the dead fish.

How often do you perform water changes? This is the main way to control water quality. You should perform weekly water changes somewhere in the range of 35%-50%.

Don't use any ph adjusting chemicals.....no matter what the person at the store tells you. What is your tap ph?

How are you acclimating the fish when you bring them home?Ben(Jrman)Has a sticky on drip acclimation,which I think would be a good read through for you.

As he said waterchanges are vital to the health of a tank.I do weekly 50% changes on my tanks and the water stays very clean.

On cycling,it can be confusing thats for sure.But basically all you need to remember is how to test your water and what to look for.You need to add a source of ammonia,in which case you have the pleco.I would not add anyone else until the cycle is complete.

Once you get the master test kit,check the ammonia,nitrite and nitrate levels.

After the cycle is finished and the readings are good,then you can get another Jack Dempsy.Drip acclimate him as per the sticky and he should do well.

Its alot to learn and I really wish petshops would have a giant sign explaining how much work they are and the proper way to set one up to be successful.

__________________
http://bountifulbettas.blogspot.com/

"Come to the dark side....we have cookies...and filters/heaters/and water changes!"

how much filtration do you have on the tank? undergravel filters aren't really reliable enough to keep cichlids in, plus with the pleco, I wouldn't be suprised if you don't have enough filtration since plecos produce a lot of waste. Find out your water parameters ASAP and you might be able to find out whats going on. it could be a lot of things. you can add things like plants and some rocks to lower your PH and to bump it up, you can add other rocks that raise PH or add some crushed coral to your filter if you need to raise it.

__________________
Frontosa Fanatic

With dempsy's you're going to have a hard time with live plants.. I'm betting your nitrates are sky high.. Without plants you have to resort to w/c's... Me?.. I do new worlds and do NO W/C's.. just replenishment needed due to vacuuming.. Discus and multiple breeding angels.. Bill in Va.

__________________
12 Tanks, 900 gallons. Discus/Angels/Malawi/Lake Victorias. Just added a 135 & 2 - 29's..